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  • 1990-1994  (742)
  • 1920-1924
  • 1991  (742)
  • Biochemistry and Biotechnology  (742)
  • 1
    Electronic Resource
    Electronic Resource
    Computational studies of ligand diffusion in globins: I. Leghemoglobin (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 70-80 
    Details
    ISSN: 0887-3585
    Keywords: locally enhanced sampling ; molecular dynamics ; ligand penetration ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The thermally assisted diffusion of a small ligand (carbon monoxide) through a protein matrix (lupine leghemoglobin) is investigated computationally. The diffusion paths are calculated by a varient of the time-dependent Hartree approximation which we call LES (locally enhanced sampling). The variant which was recently introduced by Elber and Karplus1 is based on the classical TD-SCF approximation of Gerber et al.2 The simulation enables more significant search for diffusion pathways than was possible before. This is done by increasing the number of ligand trajectories using a single trajectory for the protein. We compare qualitatively diffusion rates in leghemoglobin and in myoglobin. The calculation shows that the diffusion in leghemoglobin is much faster than the diffusion in myoglobin, in agreement with experiment. The gate in leghemoglobin is opened by fluctuations at a close contact between the B/C and the G helices. The most relevant fluctuation is the rigid shift of the C helix with respect to the G helix. This path is not observed in a comparable calculation for myoglobin.1 This finding is rationalized by the lack of the D helix in leghemoglobin and a significantly more flexible CE loop. Supporting experimental evidence for the importance of the CE loop in leghemoglobin can be found in the kinetics studies of Gibson et al.28
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340100107
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  • 2
    Electronic Resource
    Electronic Resource
    The adaptability of the active site of trypanosomal triosephosphate isomerase as observed in the crystal structures of three different complexes (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 50-69 
    Details
    ISSN: 0887-3585
    Keywords: TIM ; protein-ligand complexes ; water involvement in binding ; drug design ; active site structure ; sleeping sickness ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Crystals of triosephosphate isomerase from Trypanosoma brucei brucei have been used in binding studies with three competitive inhibitors of the enzyme's activity. Highly refined structures have been deduced for the complexes between trypanosomal triosephosphate isomerase and a substrate analogue (glycerol-3-phosphate to 2.2 Å), a transition state analogue (3-phosphonopropionic acid to 2.6 Å), and a compound structurally related to both (3-phosphoglycerate to 2.2 Å). The active site structures of these complexes were compared with each other, and with two previously determined structures of triosephosphate isomerase either free from inhibitor or complexed with sulfate. The comparison reveals three conformations available to the “flexible loop” near the active site of triosephosphate isomerase: open (no ligand), almost closed (sulfate), and fully closed (phosphate/phosphonate complexes). Also seen to be sensitive to the nature of the active site ligand is the catalytic residue Glu-167. The side chain of this residue occupies one of two discrete conformations in each of the structures so far observed. A “swung out” conformation unsuitable for catalysis is observed when sulfate, 3-phosphoglycerate, or no ligand is bound, while a “swung in” conformation ideal for catalysis is observed in the complexes with glycerol-3-phosphate or 3-phosphonopropionate. The water structure of the active site is different in all five structures. The results are discussed with respect to the triosephosphate isomerase structure function relationship, and with respect to an on-going drug design project aimed at the selective inhibition of glycolytic enzymes of T. brucei.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340100106
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  • 3
    Electronic Resource
    Electronic Resource
    The mutation β99 Asp-Tyr stabilizes Y - A new, composite quaternary state of human hemoglobin (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 81-91 
    Details
    ISSN: 0887-3585
    Keywords: mutant hemoglobin ; cooperativity ; protein structure ; conformational change ; quaternary structure ; allosteric proteins ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Carbonmonoxy hemoglobin Ypsilanti (β99 Asp-Tyr) exhibits a quaternary form distinctly different from any structures previously observed for human hemoglobins. The relative orientation of αβ dimers in the new quaternary form lies well outside the range of values observed for normal unliganded and liganded tetramers (Baldwin, J., Chothia, C., J. Mol. Biol. 129:175-220, 1979). Despite this large quaternary structural difference between carbonmonoxy hemoglobin Ypsilanti and the two canonical structures, the new quaternary structure's hydrogen bonding interactions in the “switch” region, and packing interactions in the “flexible joint” region, show noncovalent interactions characteristic of the α1β2 contacts of both unliganded and liganded normal hemoglobins. In contrast to both canonical structures, the β97 histidine residue in carbonmonoxy hemoglobin Ypsilanti is disengaged from quaternary packing interactions that are generally believed to enforce two-state behavior in ligand binding. These features of the new quaternary structure, denoted Y, may therefore be representative of quaternary states that occur transiently along pathways between the normal unliganded, T, and liganded, R, hemoglobin structures.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340100202
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  • 4
    Electronic Resource
    Electronic Resource
    The crystal structure of staphylococcal nuclease refined at 1.7 Å resolution (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 92-105 
    Details
    ISSN: 0887-3585
    Keywords: protein structure ; ligand binding ; crystallographic refinement ; phosphodiesterase ; calcium ligands ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The crystal structure of staphylococcal nuclease has been determined to 1.7 Å resolution with a final R-factor of 16.2% using stereochemically restrained Hendrickson-Konnert least-squares refinement. The structure reveals a number of conformational changes relative to the structure of the ternary complex of staphylococcal nuclease1,2 bound with deoxythymidine-3′,5′-diphosphate and Ca2+. Tyr-113 and Tyr-115, which pack against the nucleotide base in the nuclease complex, are rotated outward creating a more open binding pocket in the absence of nucleotide. The side chains of Ca2+ ligands Asp-21 and Asp-40 shift as does Glu-43, the proposed general base in the hydrolysis of the 5′-phosphodiester bond. The significance of some changes in the catalytic site is uncertain due to the intrusion of a symmetry related Lys-70 side chain which hydrogen bonds to both Asp-21 and Glu-43. The position of a flexible loop centered around residue 50 is altered, most likely due to conformational changes propagated from the Ca2+ site. The side chains of Arg-35, Lys-84, Tyr-85, and Arg-87, which hydrogen bond to the 3′- and 5′-phosphates of the nucleotide in the nuclease complex, are unchanged in conformation, with packing interactions with adjacent protein side chains sufficient to fix the geometry in the absence of ligand. The nuclease structure presented here, in combination with the stereochemically restrained refinement of the nuclease complex structure2 at 1.65 Å, provides a wealth of structural information for the increasing number of studies using staphylococal nuclease as a model system of protein structure and function.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340100203
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  • 5
    Electronic Resource
    Electronic Resource
    Projection of monte carlo and molecular dynamics trajectories onto the normal mode axes: Human lysozyme (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 106-116 
    Details
    ISSN: 0887-3585
    Keywords: collective motion ; hinge bending motion ; normal mode analysis ; anharmonic motion ; low-frequency motion ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A method is presented to describe the internal motions of proteins obtained from molecular dynamics or Monte Carlo simulations as motions of normal mode variables. This method calculates normal mode variables by projecting trajectories of these simulations onto the axes of normal modes and expresses the trajectories as a linear combination of normal mode variables. This method is applied to the result of the molecular dynamics and the Monte Carlo simulations of human lysozyme. The motion of the lowest frequency mode extracted from the simulations represents the hinge bending motion very faithfully. Analysis of the obtained motions of the normal mode variables provides an explanation of the anharmonic aspects of protein dynamics as due first to the anharmonicity of the actual potential energy surface near a minimum and second to trans-minimum conformational changes.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340100204
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  • 6
    Electronic Resource
    Electronic Resource
    Free energy calculations on binding and catalysis by α-lytic protease: The role of substrate size in the P1 pocket (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 140-148 
    Details
    ISSN: 0887-3585
    Keywords: α-lytic protease ; free energy perturbation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: We present free energy calculations using molecular dynamics on different substrates of α-lytic protease in the gas phase, in solution, while forming a noncovalent Michaelis complex with the enzyme, and in a tetrahedral structure representing a transition state/intermediate for acylation by the enzyme. Various P1 substrates were studied, with P1 = Gly, Ala, Val, and Leu. In qualitative agreement with experiment, the enzyme was calculated to bind and catalyze most effectively substrates with P1 = Ala over those with P1 = Gly, Val or Leu. Also, the calculated relative solvation free energies of Gly → Ala and Ala → Val were in qualitative agreement with experimental values in corresponding model systems. However, the level of quantitative agreement with experiment achieved in our earlier study of relative binding and catalysis of native subtilisin and an Asn-155 → Ala mutant was not achieved. We surmise that this is due to the greater difficulty in quantitatively simulating effects that are predominantly van der Waals and hydrophobic compared to those that are hydrogen bonding/electrostatic.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340100207
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  • 7
    Electronic Resource
    Electronic Resource
    1.59 Å structure of trypsin at 120 K: Comparison of low temperature and room temperature structures (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 171-187 
    Details
    ISSN: 0887-3585
    Keywords: cryocrystallography ; temperature factor ; serine protease structure ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The structure of a rat trypsin mutant [S195C] at a temperature of 120 K has been refined to a crystallographic R factor of 17.4% between 12.0 and 1.59 Å and is compared with the structure of the D102N mutant at 295 K. A reduction in the unit cell dimensions in going from room temperature to low temperature is accompanied by a decrease in molecular surface area and radius of gyration. The overall structure remains similar to that at room temperature. The attainable resolution appears to be improved due to the decrease in the fall off of intensities with resolution [reduction of the temperature factor]. This decreases the uncertainty in the atomic positions and allows the localization of more protein atoms and solvent molecules in the low temperature map. The largest differences between the two models occur at residues with higher than average temperature factors. Several features can be localized in the solvent region of the 120 K map that are not seen in the 295 K map. These include several more water molecules as well as an interstitial sulfate ion and two interstitial benzamidine molecules.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340100303
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  • 8
    Electronic Resource
    Electronic Resource
    Conformational changes in yeast phosphoglycerate kinase upon ligand binding: Fluorescence of a linked probe and chemical reactivity of genetically introduced cysteinyl residues (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 315-324 
    Details
    ISSN: 0887-3585
    Keywords: site-directed mutagenesis ; cysteine ; phosphoglycerate kinase ; IAEDANS ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The effects of ligands on the conformation of yeast phosphoglycerate kinase were explored by introducing cysteinyl residues at different positions in the molecule by site-directed mutagenesis. Thus several mutants were constructed, each containing a unique cysteinyl residue. Neither the conformation nor the enzyme activity was affected by the substitutions. The reactivity of the thiol groups and the fluorescence of N-acetyl-N′-(5-sulfo-1-naphtyl)ethylene-diamine covalently linked to these thiols were used to monitor the conformational changes induced upon ligand binding.It was found that the observed changes mainly involve the part of the protein located in the cleft, particularly the environment of residues 35 and 183. No alteration was observed on the external side of the protein. Only 3-Phosphoglycerate induced these conformational changes. However, when the fluorescent probe was attached to residue 377, the binding of the two substrates was required to induce a modification in the fluorescence of the probe. These results indicate that the substrates separately or together induce discrete molecular motions in phosphoglycerate kinase.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340100405
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  • 9
    Electronic Resource
    Electronic Resource
    Addendum (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 359-359 
    Details
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340100408
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  • 10
    Electronic Resource
    Electronic Resource
    Exploration of disorder in protein structures by X-ray restrained molecular dynamics (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 340-358 
    Details
    ISSN: 0887-3585
    Keywords: ribonuclease A ; crambin ; conformational disorder ; protein crystallography ; simulated annealing ; X-ray refinement ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Conformational disorder in crystal structures of ribonuclease-A and crambin is studied by including two independent structures in least-squares optimizations against X-ray data. The optimizations are carried out by X-ray restrained molecular dynamics (simulated annealing refinement) and by conventional least-squares optimization. Starting from two identical structures, the optimizations against X-ray data lead to significant deviations between the two, with rms backbone displacements of 0.45 Å for refinement of ribonuclease at 1.53 Å resolution, and 0.31 Å for crambin at 0.945 Å. More than 15 independent X-ray restrained molecular dynamics runs have been carried out for ribonuclease, and the displacements between the resulting structures are highly reproducible for most atoms. These include residues with two or more conformations with significant dihedral angle differences and alternative hydrogen bonding, as well as groups of residues that undergo displacements that are suggestive of rigid-body librations. The crystallographic R-values obtained are ≈ 13%, as compared to 15.3% for a comparable refinement with a single structure. Least-squares optimization without an intervening restrained molecular dynamics stage is sufficient to reproduce most of the observed displacements. Similar results are obtained for crambin, where the higher resolution of the X-ray data allows for refinement of unconstrained individual anisotropic temperature factors. These are shown to be correlated with the displacements in the two-structure refinements.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340100407
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  • 11
    Electronic Resource
    Electronic Resource
    Masthead (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 11 (1991) 
    Details
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340110101
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  • 12
    Electronic Resource
    Electronic Resource
    The electrostatic potential of Escherichia coli dihydrofolate reductase (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 11 (1991), S. 1-12 
    Details
    ISSN: 0887-3585
    Keywords: electrostatics ; enzyme-substrate interaction ; solvent screening ; active site potential ; structure-function relationship ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Escherichia coli dihydrofolate reductase (DHFR) carries a net charge of -10 electrons yet it binds ligands with net charges of -4 (NADPH) and -2 (folate or dihydrofolate). Evaluation and analysis of the electrostatic potential of the enzyme give insight as to how this is accomplished. The results show that the enzyme is covered by an overall negative potential (as expected) except for the ligand binding sites, which are located inside “pockets” of positive potential that enable the enzyme to bind the negatively charged ligands. The electrostatic potential can be related to the asymmetric distribution of charged residues in the enzyme.The asymmetric charge distribution, along with the dielectric boundary that occurs at the solvent-protein interface, is analogous to the situation occurring in superoxide dismutase. Thus DHFR is another case where the shape of the active site focuses electric fields out into solution.The positive electrostatic potential at the entrance of the ligand binding site in E. coli DHFR is shown to be a direct consequence of the presence of three positively charged residues at positions 32, 52, and 57-residues which have also been shown recently to contribute significantly to electronic polarization of the ligand folate. The latter has been postulated to be involved in the catalytic process. A similar structural motif of three positively charged amino acids that gives rise to a positive potential at the entrance to the active site is also found in DHFR from chicken liver, and is suggested to be a common feature in DHFRs from many species. It is noted that, although the net charges of DHFRs from different species vary from +3 to -10, the enzymes are able to bind the same negatively charged ligands, and perform the same catalytic function.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340110102
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  • 13
    Electronic Resource
    Electronic Resource
    Functionality maps of binding sites: A multiple copy simultaneous search method (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 11 (1991), S. 29-34 
    Details
    ISSN: 0887-3585
    Keywords: drug-design ; ligand-binding ; hemagglutinin ; functional groups ; MCSS ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A new method is proposed for determining energetically favorable positions and orientations for functional groups on the surface of proteins with known three-dimensional structure. From 1,000 to 5,000 copies of a functional group are randomly placed in the site and subjected to simultaneous energy minimization and/or quenched molecular dynamics. The resulting functionality maps of a protein receptor site, which can take account of its flexibility, can be used for the analysis of protein ligand interactions and rational drug design. Application of the method to the sialic acid binding site of the influenza coat protein, hemagglutinin, yields functional group minima that correspond with those of the ligand in a cocrystal structure.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340110104
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  • 14
    Electronic Resource
    Electronic Resource
    Relaxation data in NMR structure determination: Model calculations for the lysozyme-Gd3+ complex (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 117-129 
    Details
    ISSN: 0887-3585
    Keywords: protein NMR ; distance restraints ; paramagnetic relaxation ; protein structure determination ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The effect of including paramagnetic relaxation data as additional restraints in the determination of protein tertiary structures from NMR data has been explored by a systematic series of model calculations. The system used for testing the method was the 2.0 Å resolution tetragonal crystal structure of hen egg white lysozyme (129 amino acid residues) and structures were generated using a version of the hybrid “distance geometry-dynamic simulated annealing” procedure. A limited set of 769 NOEs was used as restraints in all the calculations; the strengths of these were categorized into three classes on the basis of distances observed in the crystal structure. The values of 50 φ angles were also restrained on the basis of amide-alpha coupling constants calculated from the X-ray structure. Five sets of 12 structures were determined using differing sets of paramagnetic relaxation data as restraints additional to those involving the NOE and coupling constant data. The paramagnetic relaxation data were modeled on the basis of the distances of defined protons from the crystallographic binding site of Gd3+ in lysozyme. Analysis of the results showed that the relaxation data significantly improved the correspondence between the set of generated structures and the crystal structure, and that the more well defined the relaxation data, the more significant the improvement in the quality of the structures. The results suggest that the inclusion of paramagnetic relaxation restraints could be of significant value for the experimental determination of protein structures from NMR data.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340100205
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  • 15
    Electronic Resource
    Electronic Resource
    The future at proteins (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. i 
    Details
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340100302
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  • 16
    Electronic Resource
    Electronic Resource
    On the multiple-minima problem in the conformational analysis of polypeptides. V. Application of the self-consistent electrostatic field and the electrostatically driven monte carlo methods to bovine pancreatic trypsin inhibitor (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 188-198 
    Details
    ISSN: 0887-3585
    Keywords: empirical potentials ; energy calculations ; protein structure prediction ; protein folding ; minimization ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: In connection with the accompanying paper to test various models for the hydration of polypeptides, we have explored a limited portion of the conformational energy hyperspace of the small protein bovine pancreatic trypsin inhibitor (BPTI) with the aid of two search methods developed in this laboratory. A series of low-energy conformations was obtained as a result of this study. These conformations constitute a set of local minima in the conformational energy space of the molecule as described by the ECEPP/2 (Empirical Conformational Energy Program for Peptides) potential energy function, without the inclusion of hydration. Five different initial conformations were used in this exploration: the first corresponds to an energy-refined structure based on the crystallographic coordinates (4PTI) provided by Deisenhofer and Steigemann25 and reported previously by Meirovitch and Scheraga.3 The remaining four initial conformations were obtained by using a Variable-Target-Function procedure, applied to the experimental Cartesian coordinates (5PTI) reported by Wlodawer et al.26The self-consistent electrostatic field (SCEF) and the electrostatically driven Monte Carlo (EDMC) methods were used to search the conformational space. The SCEF and EDMC methodologies assume that a polypeptide or protein molecule is driven toward the native structure mainly by the action of the electrostatic interactions. Application of these methodologies led to a set of conformations (up to 50 kcal/mol lower than the starting ones) with ECEPP/2 energies lower than any of those that we had previously found. Application of both methods to the initial conformation generated from 4PTI led to a series of low-energy conformations exhibiting similar rms deviations with respect to the experimental data (4PTI) as did the starting conformation. However, statistical analysis of the runs that had started from the conformations generated by using the variable-target-function procedure (and applying the EDMC method) indicated that the rms deviations of the atomic positions of the new low-energy conformations tended to increase as the energy improved, when compared with the X-ray data from which the starting conformations had been generated. The structures with the lowest energies also had radii of gyration smaller than the experimentally observed one. These results indicated a need to include hydration in the potential function, and provided the conformations used in the accompanying paper to test various hydration models.
    Additional Material: 6 Tab.
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    URL: http://dx.doi.org/10.1002/prot.340100304
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  • 17
    Electronic Resource
    Electronic Resource
    Secondary structure-based profiles: Use of structure-conserving scoring tables in searching protein sequence databases for structural similarities (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 229-239 
    Details
    ISSN: 0887-3585
    Keywords: profile method ; sequence comparison ; secondary structure-based profile ; protein sequence data bases ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The profile method, for detecting distantly related proteins by sequence comparison, has been extended to incorporate secondary structure information from know X-ray structures. The sequence of a known structure is aligned to sequences of other members of a given folding class. From the known structure, the secondary structure (α-helix, β-strand or “other”) is assigned to each position of the aligned sequences. As in the standard profile method,1 a position-dependent scoring table, termed a profile, is calculated from the aligned sequences. However, rather than using the standard Dayhoff mutation table in calculating the profile, we use distinct amino acid mutation tables for residues in α-helices, β-strands or other secondary structures to calculate the profile. In addition, we also distinguish between internal and external residues. With this new secondary structure-based profile method, we created a profile for eight-stranded, antiparallel β barrels of the insecticyanin folding class. It is based on the sequences of retinol-binding protein, insecticyanin and β-lactoglobulin. Scanning the sequence database with this profile, it was possible to detect the sequence of avidin. The structure of streptavidin is known, and it appears to be distantly related to the antiparallel β barrels. Also detected is the sequence of complement component C8, which we therefore predict to be a member of this folding class.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340100307
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  • 18
    Electronic Resource
    Electronic Resource
    Crystallographic refinement of ricin to 2.5 Å (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 240-250 
    Details
    ISSN: 0887-3585
    Keywords: ricin ; refinement ; molecular dynamics ; molecular models ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The plant cytotoxin ricin consists of two disulfide-linked chains, each of about 30,000 daltons. An initial model based on a 2.8 Å MIR electron density map has been refined against 2.5 Å data using rounds of hand rebuilding coupled with either a restrained least squares algorithm or molecular dynamics (XPLOR). The last model (9) has an R factor of 21.6% and RMS deviations from standard bond lengths and angles of 0.021 Å and 4.67°, respectively. Refinement required several peptide segments in the original model to be adjusted translationally along the electron density. A wide range of lesser changes were also made. The RMS deviation of backbone atoms between the original and model 9 was 1.89 Å. Molecular dynamics proved to be a very powerful refinement tool. However, tests showed that it could not replace human intervention in making adjustments such as local translations of the peptide chain. The R factor is not a completely satisfactory indicator of refinement progress; difference Fouriers, when observed carefully, may be a better monitor.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340100308
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  • 19
    Electronic Resource
    Electronic Resource
    Structure of ricin B-chain at 2.5 Å resolution (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 260-269 
    Details
    ISSN: 0887-3585
    Keywords: ricin toxin ; B-chain ; galactose binding ; molecular evolution ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The heterodimeric plant toxin ricin has been refined to 2.5 Å resolution. The B-chain lectin (RTB) is described in detail. The protein has two major domains, each of which has a galactose binding site. RTB has no regular secondary structure but displays several Ω loops. Each RTB domain is made of three copies of a primitive 40 residue folding unit, which pack around a pseudo threefold axis. In each domain, galactose binds in a shallow cleft formed by a three residue peptide kink on the bottom and an aromatic ring on the top. At the back of the cleft, an aspartate forms hydrogen bonds to the C3 and C4 hydroxyls of galactose, whereas a glutamine bonds to the C4 alcohol, helping to define specific epimer binding. In addition to analyzing the sugar binding mechanism, the assembly of subdomain units around the pseudo threefold axis of each domain is described. The subdomains contribute conserved Trp, Leu, and Ile residues to a compact central hydrophobic core. This tight threefold binding probably drives the peptide folding and stabilizes the protein structure.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340100310
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    Electronic Resource
    Electronic Resource
    Structure of ricin A-chain at 2.5 Å (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 251-259 
    Details
    ISSN: 0887-3585
    Keywords: Ricin A-chain ; x-ray structure ; active site ; conserved residues ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Ricin has been refined in a crystallographic sense to 2.5 Å resolution and the model for the A-chain (RTA) is described in detail. Because RTA is the first member of the class of plant toxins to be analyzed, this model probably defines the major structural characteristics of the entire family of these medically important proteins. Explanations are provided to rationalize amino acids that are conserved between RTA and a number of homologous plant and bacterial toxins. Eight invariant residues appear to be involved in creating or stabilizing the active site. In the active site Arg180 and Glu177 are hydrogen bonded to each other and also coordinate a water molecule; each of these groups may be important in the N-glycosidation reaction. Several other polar residues may play lesser roles in the mechanism, including tyrosines 80 and 123 and asparagines 78 and 209. A number of conserved hydrophobic residues are seen to cluster within several patches and probably drive the overall folding of the toxin molecule.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340100309
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    Electronic Resource
    Electronic Resource
    Masthead (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991) 
    Details
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340100401
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    Site-directed mutagenesis of ricin A-chain and implications for the mechanism of action (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 270-278 
    Details
    ISSN: 0887-3585
    Keywords: ricin A ; site-directed mutagenesis ; mechanism of action ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Ricin A-chain is an N-glycosidase that attacks ribosomal RNA at a highly conserved adenine residue. The enzyme is representative of a large family of medically significant proteins used in the design of anticancer agents and in the treatment of HIV infection. The x-ray structure has been used as a guide to create several active site mutations by directed mutagenesis of the cloned gene. Glu177 is a key catalytic residue, and conversion to Gln reduces activity 180-fold. Asn209 is shown to participate in substrate binding by kinetic analysis. Conversion to Ser increases Km sixfold but has no effect on kcat. Conversion of Tyr80 and Tyr123 to Phe decreases activity by 15- and 7-fold respectively. A mechanism of action is proposed that involves binding of the substrate adenine in a syn configuration that resembles the transition state; the putative oxycarbonium ion is probably stabilized by interaction with Glu177.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340100311
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    Electronic Resource
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    Active site conformation in myoglobin as determined by X-ray absorption spectroscopy (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 279-286 
    Details
    ISSN: 0887-3585
    Keywords: myoglobin ; structure of the active site ; XAFS Debye-Waller factor ; Einstein model ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: X-ray absorption fine structure experiments were performed to study structural and dynamic aspects of the active site of various forms of myoglobin. The structures determined for deoxyMb, MbCO, and MbO2 are consistent with the structure established by X-ray absorption fine structure experiment and X-ray crystallography. The first shell of ferrous MbNO determined contains 5 nitrogens located at 2.02 Å and a short NO bond length of 1.76 Å. This study focuses on the change of the XAFS Debye-Waller factor with temperature, which is a measure of thermal and static disorder. It was found that the changes of Debye-Waller factor with temperature for the Mb proteins, except deoxyMb, are consistent with a simple Einstein model, in which a single frequency was assumed for the bond stretching modes. In contrast, the temperature dependence of deoxyMb cannot be fitted to the Einstein model and a large disorder was found at low temperatures, which indicates the existence of conformational substates of the active site.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340100402
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    Physical reasons for secondary structure stability: α-Helices in short peptides (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 287-299 
    Details
    ISSN: 0887-3585
    Keywords: polypeptides ; α-helix ; secondary structure ; protein folding ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: It was recently found that some short peptides (including C- and S-peptide fragments of RNase A) can have considerable helicity in solution, 1-12 which was considered to be surprising. Does the observed helicity require a new explanation, or is it consistent with previous understanding? In this work we show that this helicity is consistent with the physical theory of secondary structure12-19 based on an extension of the conventional Zimm-Bragg model.20 Without any special modifications, this theory explains reasonably well almost all the experimentally observed dependencies of helicity on pH, temperature, and amino acid replacements. We conclude that the observed “general level” of helicity of C- and S-peptides (5-30% at room temperature and 10-50% near 0°C) is “normal” for short peptides consisting mainly of helix-forming and helix-indifferent residues. The helicity is modified by a multitude of weak specific side chain interactions, many of which are taken into account by the present theory;13-19 some discrepancies between the theory and experiment can be explained by weak side-chain-side chain interactions that were neglected. A reasonable coincidence of the theory with experiment suggests that it had been used to investigate the role of local interactions in the formation of α-helical “embryos” in unfolded protein chains.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340100403
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    Electronic Resource
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    Variation of folded polypeptide surface area with probe size (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 300-314 
    Details
    ISSN: 0887-3585
    Keywords: accessible area ; contact area ; molecular surface ; fractal dimension ; helices ; globins ; variable probe radius ; analytical surface models ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Three types of polypeptide surface area (contact, accessible, and molecular) have been studied as a function of the radius of a probe sphere used to map the surface. The surfaces are: (1) three α-helices, the H-helix of myoglobin, the E-helix of leghemoglobin, and an artificial polyalanine helix, each with 26 residues; (2) two globins, myoglobin and leghemoglobin, each with 153 residues: and (3) a two center model system for which the three types of surface area have been calculated analytically. The two globin helices have almost identical surface areas as a function of probe size as do the two globins. The polyalanine helix surface area is smaller but similar in shape to the globin helix areas. All three helix contact areas tend to the same limit as the probe size increases, and the globin contact areas behave similarly. Fractal dimensions were calculated for the helix and globin contact and molecular surfaces. All fractal dimensions showed strong dependence on probe size. The contact fractal dimension peaks at larger values for both the helices and globins. Most residues do not make contact with large probes (15 Å).
    Additional Material: 13 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340100404
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    Comparative analysis of the sequences and structures of HIV-1 and HIV-2 proteases (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 325-339 
    Details
    ISSN: 0887-3585
    Keywords: retroviral proteases ; aspartic proteases ; HIV ; protease inhibitors ; sequence analysis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The different isolates available for HIV-1 and HIV-2 were compared for the region of the protease (PR) sequence, and the variations in amino acids were analyzed with respect to the crystal structure of HIV-1 PR with inhibitor. Based on the extensive homology (39 identical out of 99 residues), models were built of the HIV-2 PR complexed with two different aspartic protease inhibitors, acetylpepstatin and a renin inhibitor, H-261. Comparison of the HIV-1 PR crystal structure and the HIV-2 PR model structure and the analysis of the changes found in different isolates showed that correlated substitutions occur in the hydrophobic interior of the molecule and at surface residues involved in ionic or hydrogen bond interactions. The substrate binding residues of HIV-1 and HIV-2 PRs show conservative substitutions of four residues. The difference in affinity of HIV-1 and HIV-2 PRs for the two inhibitors appears to be due in part to the change of Val 32 in HIV-1 PR to Ile in HIV-2 PR.
    Additional Material: 14 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340100406
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    Electronic Resource
    Electronic Resource
    Masthead (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 9 (1991) 
    Details
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340090101
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    Predicted three-dimensional structure of the protease inhibitor domain of the Alzheimer's disease β-amyloid precursor (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 9 (1991), S. 1-11 
    Details
    ISSN: 0887-3585
    Keywords: protein modeling ; protein homology ; trypsin ; bovine pancreatic trypsin inhibitor ; protein electrostatics ; amyloid protease inhibitor domain ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Alzheimer's disease is characterized by the deposition of amyloid β-protein as plaques and tangles in the brains of its victims. The amyloid precursor can be expressed with or without the inclusion of a protease inhibitor domain, the potential role of which in amyloidogenesis has prompted the generation of a model of its three-dimensional structure based on the known structure of a related inhibitor. The model structure predicts that the mutated residues are almost entirely on the surface of the inhibitor domain, while conserved residues constitute the hydrophobic core. In addition, several pairs of structurally complementary, or concerted, mutations are seen. These structural features provide strong evidence for the validity of the modeled structure, and it is suggested that the presence of complementary mutations may be used as a criterion for evaluating protein structures built by homology, in addition to the (spatial) location of the mutations. The terminal residues delimiting the domain are among those furthest from the protease binding site and are in close proximity to one another, thus suggesting the ability of the domain to function as a structural cassette within the context of a larger protein. The electrostatic potentials of the inhibitor and of the related bovine pancreatic trypsin inhibitor reveal how two inhibitors with very different net charges can bind with approximately the same binding constant to trypsin and suggest a mutation of trypsin that might selectively enhance the binding of the amyloid inhibitor domain. The model provides a structural basis for understanding the functional roles of residues in the domain and for designing simpler molecules to test as pharmacologic agents for intervention in Alzheimer's disease.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340090102
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    Rate of β-structure formation in polypeptides (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 9 (1991), S. 23-27 
    Details
    ISSN: 0887-3585
    Keywords: polypeptides ; protein folding ; β-structure ; free energy barrier ; nucleation of folding ; rate-limiting step ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: An explanation is suggested for why a marginally stable β-structure folds extremely slowly; it is predicted that even a small increase in stability drastically accelerates β-folding. According to the theory, this folding is a first-order phase transition, and the rate-limiting step is nucleation. The rate-determining “nucleus” (transition state) is the smallest β-sheet that is sufficiently large to provide an overall free energy reduction during subsequent folding. If the stability of the β-structure is low, the nucleus is large and possesses a high free energy due to having a large perimeter. When the net stability of the final β-structure increases (due to either an increase of the β-sheet stability or a decrease in stability of the competing structures, e.g., α-helices), the size and energy of a nucleus decrease and the rate of folding increases exponentially. This must result in a fast folding of polypeptides enriched by β-forming residues (e.g., protein chains). The theory is developed for intramolecular β-structure, but it can also explain the overall features of intermolecular β-folding; it is applicable both to antiparallel and parallel β-sheets. The difference in folding of β-sheets, α-helices, and proteins is discussed.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340090104
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    Design and synthesis of the pseudo-EF hand in calbindin D9K: Effect of amino acid substitutions in the α-helical regions (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 9 (1991), S. 12-22 
    Details
    ISSN: 0887-3585
    Keywords: calbindin D9K ; pseudo-EF hand ; peptide synthesis ; peptide design ; calcium ; α-helix ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A series of 37-residue analogues of the pseudo-EF hand in bovine calbindin D9K has been synthesized by the solid phase method. In the presence of calcium an α-helical induction of up to 44% was observed for the peptide with the native sequence with a Kd for calcium binding of 0.35 mM. A number of amino acid substitutions have been carried out to study the packing of the two α-helices based on the crystal structure of the entire protein. Three strategies were employed: (1) replacement of the Leu residues, which in the crystal structure do not contribute to the hydrophobic interaction between the two helices, by Gln or Ala in order to control the orientation of the helix packing, (2) stabilization of the individual helix by introducing a Glu-…Lys+ salt bridge or by changing the N-terminal charge to compensate for the helix dipole moment, and (3) introduction of a disulfide bond between the two helices to help the packing of the helices.The mutants with the substitution of (Leu-30, Leu-32) to (Gln-30, Gln-32), (Gln-30, Ala-32), and (Ala-30, Ala-32) designed based on the strategy 1 do not show any affinity for calcium and have low α-helicity. The Leu-30 to Lys-30 mutant designed to form a salt bridge between the side chains of Glu-26 and Lys-30 has an apparent Kd for calcium of 6.8 mM. Kd of the N-terminal acetylated and succinylated mutants are 0.41 and 0.45 mM, respectively, and no increase in the α-helix content relative to that of the natural sequence peptide is observed. The disulfide containing mutants, namely Tyr-13, Leu-31 to Cys-31 and Tyr-13, Leu-31 to Cys-13, hCys-31, show apparent Kd values of 0.93 and 2.1 mM, respectively. The former mutant shows the highest α-helix content among the peptides studied in the presence and absence of calcium. While it is difficult to construct an isolated and rigid helix-loop-helix motif with peptides of this size, introduction of a disulfide bond proved to be effective for this purpose.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340090103
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    Modelling the three-dimensional structure and electrostatic potential field of the two Cu,Zn superoxide dismutase variants from xenopus laevis (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 149-155 
    Details
    ISSN: 0887-3585
    Keywords: Cu,Zn superoxide dismutase ; model building ; protein structure-function ; Poisson-Boltzmann ; electrostatic potentials ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The crystallographic structure of bovine superoxide dismutase has been used as a template for the graphic reconstruction of the three-dimensional structures of the two Xenopus laevis variants (Schinina', M. E. et al. Arch. Biochem. Biophys. 272:507-515, 1989). In these models the structure-essential residues maintain their position and their structural role, and the interactions between the subunits and the close packing within the β-barrel are maintained with conservative substitutions and even increased with “aromatic pairs.” Because of the same topological motif and surface location of charges, arising from the model building of the two variants with respect to the bovine enzyme, we have calculated the electrostatic potential fields around the models of the two Xenopus laevis variants by numerically solving the Poisson-Boltzmann equation. We show that conservation of a specific space-relationship of charges maintains the potential field pattern already observed in the bovine enzyme, where a negative potential field surrounds the protein surface and specific positive regions wrap up the copper center active site. This electrostatic potential field distribution supports the idea that electrostatic interactions control, like in the bovine enzyme, the mechanism of enzyme-substrate recognition in the Xenopus laevis Cu,Zn superoxide dismutases, suggesting that coordinated mutation of charged residues has occurred in the evolution of this enzyme.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340100208
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    Cu(II)-Binding properties of a cytochrome c with a synthetic metal-binding site: His-X3-His in an α-helix (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 156-161 
    Details
    ISSN: 0887-3585
    Keywords: synthetic metalloproteins ; protein engineering ; iso-1-cytochrome c ; metal binding ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A metal-binding site consisting of two histidines positioned His-X3-His in an α-helix has been engineered into the surface of Saccharomyces cerevisiae iso-1-cytochrome c. The synthetic metal-binding cytochrome c retains its biological activity in vivo. Its ability to bind chelated Cu(II) has been characterized by partitioning in aqueous two-phase polymer systems containing a polymer-metal complex, Cu(II)IDA-PEG, and by metal-affinity chromatography. The stability constant for the complex formed between Cu(II)IDA-PEG and the cytochrome c His-X3-His site is 5.3 × 104 M-1, which corresponds to a chelate effect that contributes 1.5 kcal mol-1 to the binding energy. Incorporation of the His-X3-His site yields a synthetic metal-binding protein whose metal affinity is sensitive to environmental conditions that alter helix structure or flexibility.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340100209
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    Proline in α-helix: Stability and conformation studied by dynamics simulation (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 219-228 
    Details
    ISSN: 0887-3585
    Keywords: proline ; α-helix ; kinked α-helix ; molecular dynamics ; computer simulation ; peptide conformation stability ; protein conformational stability ; amino acid substitution ; protein architecture ; helix start/stop signal ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Free-energy simulations have been used to estimate the change in the conformational stability of short polyalanine α-helices when one of the alanines is replaced by a proline residue. For substituting proline in the middle of the helix the change in free energy of folding (ΔΔG°) was calculated as 14 kJ/mol (3.4 kcal/mol), in excellent agreement with the one available experimental value. The helix containing proline was found to be strongly kinked; the free energy for reducing the angle of the kink from 40° to 15° was calculated, and found to be small. A tendency to alternate hydrogen bonding schemes was observed in the proline-containing helix. These observations for the oligopeptide agree well with the observation of a range of kink angles (18-35°) and variety of hydrogen bonding schemes, in the rare instances where proline occurs in helices in globular proteins. For substituting proline at the N-terminus of the helix the change in free energy of folding (ΔΔG°) was calculated as -4 kJ/mol in the first helical position (N1) and +6 kJ/mol in the second helical position (N2). The observed frequent occurrence of proline in position N1 in α-helices in proteins therefore has its origin in stability differences of secondary structure. The conclusion reached here that proline may be a better helix former in position N1 than (even) alanine, and thus be a helix initiator may be testable experimentally by measurements of fraction helical conformation of individual residues in oligopeptides of appropriate sequence. The relevance of these results in regards to the frequent occurrence of proline-containing helices in certain membrane proteins is discussed.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340100306
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    Empirical solvation models can be used to differentiate native from near-native conformations of bovine pancreatic trypsin inhibitor (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 199-218 
    Details
    ISSN: 0887-3585
    Keywords: empirical potentials ; energy calculations ; surface area ; protein stability ; protein folding ; protein structure prediction ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Several hydration models for peptides and proteins based on solvent accessible surface area have been proposed previously. We have evaluated some of these models as well as four new ones in the context of near-native conformations of a protein. In addition, we propose an empirical site-site distance-dependent correction that can be used in conjuction with any of these models.The set of near-native structures consisted of 39 conformations of bovine pancreatic trypsin inhibitor (BPTI) each of which was a local minimum of an empirical energy function (ECEPP) in the absence of solvent. Root-mean-square (rms) deviations from the crystallographically determined structure were in the following ranges: 1.06-1.94 Å for all heavy atoms, 0.77-1.36 Å for all backbone heavy atoms, 0.68-1.33 Å for all α-carbon atoms, and 1.41-2.72 Å for all side-chain heavy atoms.We have found that there is considerable variation among the solvent models when evaluated in terms of concordance between the solvation free energy and the rms deviations from the crystallographically determined conformation. The solvation model for which the best concordance (0.939) with the rms deviations of the Cα atoms was found was derived from NMR coupling constants of peptides in water combined with an exponential site-site distance dependence of the potential of mean force.Our results indicate that solvation free energy parameters derived from nonpeptide free energies of hydration may not be transferrable to peptides. Parameters derived from peptide and protein data may be more applicable to conformational analysis of proteins. A general approach to derive parameters for free energy of hydration from ensemble-averaged properties of peptides in solution is described.
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    URL: http://dx.doi.org/10.1002/prot.340100305
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    Structural and functional relations among thioredoxins of different species (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 11 (1991), S. 13-28 
    Details
    ISSN: 0887-3585
    Keywords: thiol-dependent redox proteins ; redox-active disulfide ; sequence homology ; three-dimensional structure ; molecular modeling ; protein domains ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Three-dimensional models have been constructed of homologous thioredoxins and protein disulfide isomerases based on the high resolution x-ray crystallographic structure of the oxidized form of Escherichia coli thioredoxin. The thioredoxins, from archebacteria to humans, have 27-69% sequence identity to E. coli thioredoxin. The models indicate that all the proteins have similar three-dimensional structures despite the large variation in amino acid sequences. As expected, residues in the active site region of thioredoxins are highly conserved. These include Asp-26, Ala-29, Trp-31, Cys-32, Gly-33, Pro-34, Cys-35, Asp-61, Pro-76, and Gly-92. Similar residues occur in most protein disulfide isomerase sequences. Most of these residues form the surface around the active site that appears to facilitate interactions with other enzymes.Other structurally important residues are also conserved. A proline at position 40 causes a kink in the alpha-2 helix and thus provides the proper position of the active site residues at the amino end of this helix. Pro-76 is important in maintaining the native structure of the molecule. In addition, residues forming the internal contact surfaces between the secondary structural elements are generally unchanged such as Phe-12, Val-25, and Phe-27.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340110103
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    Comparative modeling of mammalian aspartate transcarbamylase (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 9 (1991), S. 191-206 
    Details
    ISSN: 0887-3585
    Keywords: CAD ; E. coli ATCase ; energy minimization ; multifunctional proteins ; protein domains ; sequence homology ; evaluation of protein models ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Mammalian aspartate transcarbamylase (ATCase) is part of a 243 kDa multidomain polypeptide, called CAD, that catalyzes the first three steps in de novo pyrimidine biosynthesis. The structural organization of the mammalian enzyme is very different from E. coli ATCase, a dodecameric, monofunctional molecule comprised of six copies of separate catalytic and regulatory chains. Nevertheless, sequence similarities and other properties suggested that the mammalian ATCase domain and the E. coli ATCase catalytic chain have the same tertiary fold. A model of mammalian ATCase was built using the X-ray coordinates of the E. coli catalytic chain as a tertiary template. Five small insertions and deletions could be readily accommodated in the model structure. Following energy minimization the RMS difference in the α carbon positions of the mammalian and bacterial proteins was 0.93 Å. A comparison of the hydrophobic energies, surface accessibility index, and the distribution of hydrophilic and hydrophobic residues of the CAD ATCase structure with correctly and incorrectly folded proteins and with several X-ray structures supported the validity of the model. The mammalian ATCase domain associates to form a compact globular trimer, a prerequisite for catalysis since the active site is comprised of residues from adjacent subunits. Interactions between the clearly defined aspartate and carbamyl phosphate subdomains of the monomer were largely preserved while there was appreciable remodeling of the trimeric interfaces. Several clusters of basic residues are located on the upper surface of the domain which account in part for the elevated isoelectric point (pI = 9.4) and may represent contact regions with other more acidic domains within the chimeric polypeptide. A long interdomain linker connects the monomer at its upper surface to the remainder of the polypeptide. The configuration of active site residues is virtually identical in the mammalian and bacterial enzymes. While the CAD ATCase domain can undergo the local conformational changes that accompany catalysis in the E. coli enzyme, the high activity, closed conformation is probably more stable in the mammalian enzyme.
    Additional Material: 12 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340090305
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    Electronic Resource
    Electronic Resource
    Electron redistribution on binding of a substrate to an enzyme: Folate and dihydrofolate reductase (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 9 (1991), S. 217-224 
    Details
    ISSN: 0887-3585
    Keywords: protein-ligand interactions ; electron density ; quantum mechanics ; local density functional theory ; charge polarization ; enzymatic reaction ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The migration of electron density of a substrate (folate) on binding to an enzyme (dihydrofolate reductase) is studied by a quantum-mechanical method originally developed in solid state physics. A significant polarization of the substrate is induced by the enzyme, toward the transition state of the enzymatic reaction, at the same time giving rise to “electronic strain energy” in the substrate and enhanced protein-ligand interactions. The spatial arrangement of protein charges that induces the polarization is identified and found to be structurally conserved for bacterial and vertebrate dihydrofolate reductases.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340090307
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  • 38
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    Electronic Resource
    Side chain-backbone hydrogen bonding contributes to helix stability in peptides derived from an α-helical region of carboxypeptidase A (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 130-139 
    Details
    ISSN: 0887-3585
    Keywords: α-helix ; side chain-backbone hydrogen bonding ; helix dipole ; circular dichroism ; carboxypeptidase A ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Recently, Presta and Rose proposed1 that a necessary condition for helix formation is the presence of residues at the N-and C-termini (called NTBs and CTBs) whose side chains can form hydrogen bonds with the initial four amides and the last four carbonyls of the helix, which otherwise lack intrahelical hydrogen bonding partners. We have tested this hypothesis by conformational analysis by circular dichroism (CD) of a synthetic peptide corresponding to a region (171-188) of the protein carboxypeptidase A; in the protein, residues 174 to 186 are helical and are flanked by NTBs and CTBs. Since helix formation in this peptide may also be stabilized by electrostatic interactions, we have compared the helical content of the native peptide with that of several modified peptides designed to enable dissection of different contributions to helix stability. As expected, helix dipole interactions appear to contribute substantially, but we conclude that hydrogen bonding interactions as proposed by Presta and Rose also stabilize helix formation. To assist in comparison of different peptides, we have introduced two concentration-independent CD parameters which are sensitive probes of helix formation.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340100206
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  • 39
    Electronic Resource
    Electronic Resource
    Masthead (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991) 
    Details
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340100301
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  • 40
    Electronic Resource
    Electronic Resource
    Modeling conformational change in macromolecules as an elastic deformation (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 162-170 
    Details
    ISSN: 0887-3585
    Keywords: conformation difference ; strain ; elasticity ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Macromolecules are elastic bodies. Atomic strucutres are available for nucleic acids and proteins in two or more different conformations. It is a common practice to compare two structures by finding the best rigid body superposition of the molecules. This ignores possible deformations. There is useful information in the deviations from the rigid body superposition. If the deviations are considered to be elastic deformations of a common structure than it is possible to extract this information. Results are shown for comparisons of deoxyhemoglobin versus carbonmonoxyhemoglobin and for two different conformations of catabolite gene activator protein.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340100210
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  • 41
    Electronic Resource
    Electronic Resource
    Assignment of the nucleotide binding sites and the mechanism of substrate inhibition of Escherichia coli adenylate kinase (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 9 (1991), S. 28-36 
    Details
    ISSN: 0887-3585
    Keywords: site-directed mutagenesis ; ATP and AMP binding sites ; tryptophan fluorescence ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Site-directed mutagenesis of key amino acids of adenylate kinase has been used to suggest a new model for the location of the AMP and ATP binding sites. Phe-86 and Tyr-133, which are in close contact with the inhibitor Ap5A according to previous crystallographic results, have been independently changed to tryptophan and other amino acids. The Phe-86→Trp mutant had a 3- to 6-fold change in the Km for ATP and a 44-fold increase in the Km for AMP with a simultaneous loss of AMP substrate inhibition. Thus Phe-86 is probably in close contact with bound AMP. The Tyr-133→Trp mutant showed no large effects on enzyme kinetics and suggests that the previous assignment of Ap5A occupying natural adenosine binding sites is probably incorrect. A temperature-sensitive Leu-107→Gln mutant showed a 6-fold decrease in the Km for ATP and no effect on AMP binding, suggesting that this amino acid is near the ATP binding site.Changes in the fluorescence of single tryptophan-containing mutant enzymes provided specific information about AMP and ATP binding. The fluorescence results are consistent with the kinetic studies, and also suggest that AMP substrate inhibition is caused by the formation of an abortive complex that prevents the release of product.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340090105
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    Electronic Resource
    Erratum (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 9 (1991), S. 79-79 
    Details
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340090109
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  • 43
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    Electronic Resource
    Distribution and complementarity of hydropathy in mutisunit proteins (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 9 (1991), S. 37-55 
    Details
    ISSN: 0887-3585
    Keywords: protein-protein interactions ; intersubunit binding ; hydropathy ; hydropathy complementarity ; protein interfaces ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A survey of 40 multisubunit proteins and 2 protein-protein complexes was performed to assay quantitatively the distribution of hydropathy among the exterior surface, interior, contact surface, and noncontact exterior surface of the isolated subunits. We suggest a useful way to present this distribution by using a “hydropathy level diagram.” Additionally, we have devised a function called “hydropathy complementarity” to quantitate the degree to which interacting surfaces have matching hydropathy distributions. Our survey revealed the following patters: (1) The difference in hydropathy between the interior and exterior of subunits is a fairly invariant quantity. (2) On average, the hydropathy of the contact surface is higher than that of the exterior surface, but is not greater than that of the protein as a whole. There was variation, however, among the proteins. In some instances, the contact surface was more hydrophilic than the noncontact exterior, and in a few cases the contact surface was as hydrophobic as the protein interior. (3) The average interface manifests significant hydropathy complementarity, signifying that proteins interact by placing hydrophobic centers of one surface against hydrophobic centers of the other surface, and by similarly matching hydrophilic centers. As a measure of recognition and specificity, hydropathy complementarity could be a useful tool for predicting correct docking of interacting proteins. We suggest that high hydropathy complementarity is associated with static inflexible interactions. (4) We have found that some subunits that bind predominantly through hydrophilic forces, such as hydrogen bonds, ionic pairs, and water and metal bridges, are involved in dynamic quaternary organization and allostery.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340090106
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    Electronic Resource
    Electronic Resource
    Database of homology-derived protein structures and the structural meaning of sequence alignment (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 9 (1991), S. 56-68 
    Details
    ISSN: 0887-3585
    Keywords: secondary structure ; tertiary structure ; residue conservation ; sequence variability ; sequence profile ; folding units ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The database of known protein three-dimensional structures can be significantly increased by the use of sequence homology, based on the following observations. (1) The database of known sequences, currently at more than 12,000 proteins, is two orders of magnitude larger than the database of known structures. (2) The currently most powerful method of predicting protein structures is model building by homology. (3) Structural homology can be inferred from the level of sequence similarity. (4) The threshold of sequence similarity sufficient for structural homology depends strongly on the length of the alignment. Here, we first quantify the relation between sequence similarity, structure similarity, and alignment length by an exhaustive survey of alignments between proteins of known structure and report a homology threshold curve as a function of alignment length. We then produce a database of homology-derived secondary structure of proteins (HSSP) by aligning to each protein of known structure all sequences deemed homologous on the basis of the threshold curve. For each known protein structure, the derived database contains the aligned sequences, secondary structure, sequence variability, and sequence profile. Tertiary structures of the aligned sequences are implied, but not modeled explicity. The database effectively increases the number of known protein structures by a factor of five to more than 1800. The results may be useful in assessing the structural significance of matches in sequence database searches, in deriving preferences and patterns for structure prediction, in elucidating the structural role of conserved residues, and in modeling three-dimensional detail by homology.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340090107
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  • 45
    Electronic Resource
    Electronic Resource
    Thermodynamics of ligand binding and denaturation for his64 mutants of tissue plasminogen activator kringle-2 domain (1991)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 11 (1991), S. 35-44 
    Details
    ISSN: 0887-3585
    Keywords: microcalorimetry ; thermal stability ; lysine binding ; site-directed ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The contribution of His64 to the function and stability of tissue plasminogen activator (t-PA) kringle-2 domain (His244 in t-PA numbering) has been studied by using microcalorimetric methods to compare the ligand binding and thermal denaturation behavior of wild-type kringle-2 and mutants having His64 replaced with Tyr or Phe. This site was examined because modeling studies1 suggested that the His64 side chain could play an important role in ligand binding by forming an ion-pair with the carboxylate of the ligand, L-lysine. Kringle-2 domains were expressed by secretion of the 174-263 portion of t-PA in E. coli and purified as previously described for the wild-type domain.2 Both mutant proteins retain affinity for L-lysine, although reduced three- to four-fold relative to wild-type, demonstrating that His64 does not interact with the ligand carboxylate through an ion-pair interaction or by hydrogen bonding. The H64Y substitution does result in an altered specificity of the lysine binding site with the mutant domain having greatest affinity for a ligand of 6.8 Å chain length, whereas the wild-type domain prefers an 8.8 Å long ligand. For both wild-type and mutant, the binding of the optimal chain length ligand is dominated by enthalpic effects (ΔH = -6,000 to -7,000 cal/mol) and TΔS accounts for 〈 15% of ΔG. In addition, the H64Y mutant differs from wild-type in the effect of ligand α-amino group modification on binding affinity. Based on examination of the x-ray structure recently determined for wild-type kringle-2, the specificity changes accompanying the H64Y substitution probably result from changes in side chain interactions in the lysine binding site. Thermal denaturation experiments show that the H64Y mutant is also more stable than the wild-type protein with the difference in stabilization free energy (ΔΔG) equal to 2.7 kcal/mol at 25°C and pH 3. The increased stability of the mutant appears to be related to the difference in hydrophobicity between His and Tyr.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340110105
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  • 46
    Electronic Resource
    Electronic Resource
    The effect of electrochemical regeneration upon the enzymatic catalysis of a thermodynamically unfavorable reaction (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 788-796 
    Details
    ISSN: 0006-3592
    Keywords: enzymatic electrocatalysis ; NADH ; cofactor regeneration ; product inhibition ; organic synthesis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The association between enzymatic and electrochemical reactions, enzymatic electrocatalysis, had proven to be a very powerful tooth in both analytical and synthetic fields. However, most of the combinations studied have involved enzymatic catalysis of irreversible or quasi-irreversible reaction. In the present work, we have investigated the possibility of applying enzymatic electrocatalysis to a case where the electrochemical reaction drives a thermodynamically unfavorable reversible reaction. Such thermodynamically unfavorable reactions include most of the oxidations catalyzed by dehydrogenases. Yeast alcohol dehydrogenase (E.C. 1.1.1.1) was chosen as a model enzyme because the oxidation of ethanol is thermodynamically very unfavorable and because its kinetics are well known. The electrochemical reaction was the oxidation of NADH which is particularly attractive as a method of cofactor regeneration. Both the electrochemical and enzymatic reactions occur in the same batch reactor in such a way that electrical energy is the only external driving force. Two cases were experimentally and theoretically developed with the enzyme either in solution or immobilized onto the electrode's surface. In both cases, the electrochemical reaction could drive the enzymatic reaction by NADH consumption in solution or directly in the enzyme's microenvironment. However even for a high efficiency of NADH consumption, the rate of enzymatic catalysis was limited by product (acetaldedehyde) inhibition. Extending this observation to the subject of organic synthesis catalyzed by dehydrogenases, we concluded that thermodynamically unfavorable reaction and can only be used in a process if efficient NAD regeneration and product elimination are simultaneously carried out within the reactor.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380713
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  • 47
    Electronic Resource
    Electronic Resource
    Masthead (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991) 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380801
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  • 48
    Electronic Resource
    Electronic Resource
    Production of monoclonal antibody using free-suspended and immobilized hybridoma cells: Effect of serum (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 821-830 
    Details
    ISSN: 0006-3592
    Keywords: hybridoma ; immobilization ; serum ; flow cytometry ; antibody productivity ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The effect of serum on cell growth and monoclonal antibody (MAb) productivity was studied in a repeated fedbatch mode using both free-suspended and immobilized S3H5/γ2bA2 hybridoma cells. In the suspension culture, serum influenced the cell growth rate but not the specific MAb productivity. The average specific growth rate of the suspension culture in medium containing 10% serum was approximately 0.99 ± 0.12 day-1 (±standard deviation), while that in medium containing 1% serum was approximately 0.73 ± 0.12 day-1. The specific MAb productivity was almost constant at 3.69 ± 0.57 μg/106 cells/day irrespective of serum concentration reached a maximum at ca. 1.8 × 106 cells/mL of medium in 10% serum medium, and the cell concentration was gradually reduced to 1%. The specific MAb productivity of the immobilized cells was more than three times higher than that of the free-suspended cells. The amount of serum in the medium did not influence the specific MAb production rate of the immobilized cells. The maintenance of high cell concentration and the enhanced specific MAb productivity of the immobilized cell culture resulted in a higher volumetric MAb productivity. In addition, MAb yield in the immobilized cell culture with medium containing 1% serum was 2.2 mg/mL of serum, which was approximately three times higher than that in the suspension culture.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380804
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  • 49
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    Electronic Resource
    Optimization of a two-stage recombinant fermentation process: The dilution rate effect (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 831-837 
    Details
    ISSN: 0006-3592
    Keywords: fermentation ; Escherichia coli ; recombinant fermentation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The effects of dilution rates on the performance of a two-stage fermentation system for a recombinant Escherichia coli culture were studied. Dilution rate determines the apparent or averaged specific growth rate of a heterogeneous population of cells in the recombinant culture. The specific growht rate affects the genetic parameters involved in product formation in the second stage, such as plasmid stability, plasmid content, and specific gene expression rate. Kinetic models and correlations were developed for these parameters based on experimental data. Simulations of plasmid stability in the first stage showed that for longer fermentation periods, plasmid stability is better at higher dilution rates. However, the plasmid content is lower at these dilution rates. The optimal apparent specific growth rate for maximum productivity in the second stage was determined using two methods: (1) direct search for a constant specific growth rate, and (2) dynamic optimization using the maximum principle for a time-dependent specific growth rate profile. The results of the calculations showed that the optimum constant apparent specific growth rate for maximum over-all productivity is 0.40 h-1. This coincides with the optimal specific growht rate for maximum plasmid content in the expressed stage. A 3.5% increase in overall productivity can be obtained by using a linear time dependent apparent specific growth rate control, μ2(t) = 0.0007t, in the course of the fermentation time.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380805
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  • 50
    Electronic Resource
    Electronic Resource
    Reaction kinetics in biofilms (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 877-882 
    Details
    ISSN: 0006-3592
    Keywords: microtechnique ; microprobe ; biofilm ; dissolved oxygen concentration ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A novel in situ microtechnique allows evaluating parameters of diffusion-controlled reactions in biofilms. A microprobe, 15 μm in diameter, was used to simultaneously measure the dissolved oxygen concentration and the optical density at different depths in a submerged biofilm. Based on the results, the biofilm diffusion coefficient for dissolved oxygen, Df the dissolved oxygen flux through the biofilm surface, J02, and the half velocity coefficient, Ks, have been calculated.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380809
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  • 51
    Electronic Resource
    Electronic Resource
    Fluorescence modeling in a multicomponent system (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 907-922 
    Details
    ISSN: 0006-3592
    Keywords: fluorescene monitoring ; inner-filter effect ; biosensor ; tryptophan ; tyrosine ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An extensive fluorescence database for binary tyrosinetryptophan mixtures utilizing 280 nm excitation was collected. The database spanned three orders of magnitude (10-6M-10-3M) and covered all compositions within this range. A generalized model for describing the multicomponent fluorescence signals as a function of emission wavelength, excitation wavelength, and sample composition was derived. A geometric integral that contained all the geometric factors affecting fluorescence was introduced; thus the model was applicable to various configurations, including the three used in this study: an NADH probe, a backscatter laser-induced fluorescence setup, and a commercial spectroflurometer. A correction factor was proposed that allowed linearization of the fluorescence signals with respect to fluorophore concentrations. The effect of the water Raman on fluorescence spectra was also modeled. The model contains only two wavelength-dependent parameters for each of the components present in a sample, one specifying absorption of the excitation energy and the other specifying the species' fluorescence tendency. These wavelength-dependent parameters were correlated with polynomials. The average prediction error at each wavelength was 10-20%, a major portion of which was attributed to experimental uncertainties.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380812
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  • 52
    Electronic Resource
    Electronic Resource
    Xylanase production by Aspergillus awamori. Development of a medium and optimization of the fermentation parameters for the production of extracellular xylanase and β-xylosidase while maintaining low protease production (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 883-890 
    Details
    ISSN: 0006-3592
    Keywords: Aspergillus awamori ; low protease production ; dinitrosalicylic method ; xylanase ; β-xylosidase ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A growth medium was developed for maximal production in batch culture of extracellular xylanase and β-xylosidase by Aspergillus awamori CMI 142717 and a mutant (AANTG 43) derived from the wild-type strain. The optimum pH for the production of xylanase and β-xylosidase was 4.0. The best temperature of xylanase production was 30°C; 35°C was optimal for β-xylosidase. Protease production was never completely suppressed under any of the conditions tested. However, protease titre was 3.5-fold less than the control in medium in which proteose peptone and yeast extract were omitted: the level of xylanase was not affected (8.6 U mL-1) but β-xylosidase titre was increased 4.7-fold to 1.5 U mL-1. When corn steep liquor was used as the sole nitrogen source, xylanse and β-xylosidase titres were further increased by 1.5- and 1.9-fold, respectively. Of the carbon sources investigated, ball-milled oat straw or oat spelt xylan produced the highest titres of xylanse and β-xylosidase. None of the soluble carbon sources investigated produced the high titres of xylanase or β-xylosidase induced by either oat straw for xylanse and β-xylosidase was 2% and the optimum spore inoculum was between 106 and 107 spores/mL-1 final concentration. The level of xylanse activity obtained in the culture filtrates of the mutant was a remarkable 820 U mL-1 when the reducing sugar released was measured by the dinitrosalicylic acid method. This enzyme titre would appear to be the highest reported so far. The xylanases system contained the correct balance of enzymes to effect extensive hydrolysis of oat spelt xylan. The protease titre was very low.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380810
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  • 53
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    Electronic Resource
    Kinetic analysis of cephalosporin biosynthesis in Streptomyces clavuligerus (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 941-947 
    Details
    ISSN: 0006-3592
    Keywords: Streptomyces clavuligerus ; cephalosporin ; rate-limiting enzyme ; kinetic model ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A kinetic model describing the cephalosporin biosynthesis in Streptomyces clavuligerus was developed. Using previously reported kinetic data of biosynthetic enzymes, we examined the kinetics of cephalosporin production. The predicted time profile of the specific production rate during a batch culture parallels that of experimental observation. Sensitivity analysis reveals that δ-(L-α-aminoadipyl)-L-cysteinyl-D-valine (ACV) synthetase is the rate-limiting enzyme. The effect of amplifying ACV synthetase on the specific production rate was analyzed theoretically. Increasing ACV synthetase enhances the production rate initially until ACV synthetase enhances the production rate initially until deacetocycephalosporin C hydroxylase becomes rate-limiting. Such kinetic analysis can provide a rational basis for modifying the biosynthetic machinery of cephalosporin through gene cloning.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380815
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  • 54
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    Electronic Resource
    Application of lipase to concentrate the docosahexaenoic acid (DHA) fraction of fish oil (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 956-959 
    Details
    ISSN: 0006-3592
    Keywords: Rhizopus niveus ; DHA ; omega-3 fatty acid ; specification ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A commercial lipase preparation from Rhizopus niveus was used to concentrate the omega-3 fatty acid, docosahexaenoic acid (DHA) component in fish oil. The DHA content of cod-liver oil was 9.64% (w/w) of total fatty acids. Enzymatic digestion conditions were established which produced a DHA content in the monoglycerides fraction of 29.17% (w/w) of total fatty acid, triglyceride, and diglyceride components were 5.72, 9.95, and 15316%, respectively.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380818
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    Electronic Resource
    Masthead (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991) 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380901
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  • 56
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    Differential product release (DPR) of proteins from yeast: A new technique for selective product recovery from microbial cells (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 977-985 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A novel method has been developed for the separation of bioproducts from yeast cells. The method uses a combination of physical, chemical, and biological agents such as lytic enzymes, osmotic supports, and spheroplast stabilizers. Using this technique, products (proteins and enzymes) can be released from specific cell locations at different process states; it has thus been celled differential product release (DPR). The wall-associated proteins are released first and the lytic enzyme is removed together with the wall proteins at this stage. Secondly, the cytosol products are released by a mild procedure during which the organelles remained intact. Finally, the organelle proteins are solubilized. In each stage, specific proteins are released while others are kept inside the different cell compartments. This method can be used with relatively high yeast concentrations (up to 145 g dry wt/L) and gives higher product recoveries and much higher selectivity than mechanical disruption.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380904
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  • 57
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    Inactivation and stabilization of stabilisins in neat organic solvents (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1001-1006 
    Details
    ISSN: 0006-3592
    Keywords: subtilisin ; enzymes ; inactivation ; stabilization ; organic solvents ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The stability of the serine proteases from Bacillus amyloliquefaciens (subtillisin BPN') and Bacillus licheniformis (subtilisin Carlsberg) was investigated in various anhydrous solvents at 45°C. The half-life of subtilisin BPN' in dimethyl-formamide dramatically depends on the pH of the aqueous solutions from which the enzyme was lyophilized, increasing from 48 min to 20 h when the pH is raised from 6.0 to 7.9. Both subtilisins exhibited substantial inactivation during multihour incubations in tert-amyl alcohol and acetonitrile when enzymatic activities were also measured in these solvents; however, when the enzymes were assayed in water instead, hardly any loss of activity was detected. This surprising difference appears to stem from the partitioning of the bound water essential for catalytic activity from the enzymes into the solvents. When assayed in organic solvents, this time-dependent stripping of water results in decay of enzymatic activity; however, when assayed in water, where the dehydrated subtilisins can undergo rehydration thereby recovering catalytic activity, little inactivation is observed. In agreement with this hypothesis, the addition of small quantities of water tert-amyl alcohol stabilized the subtilisins in it even when enzymatic activity was measured in the nonaqueous solvent. Ester substrates (vinyl butyrate and trichloroethyl butyrate) greatly enhanced the stability of both subtilisins in organic solvents possibly because of the formation of the acyl-enzymes.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380907
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  • 58
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    Electronic Resource
    Interaction of invertase with polyelectrolytes (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1012-1019 
    Details
    ISSN: 0006-3592
    Keywords: invertase ; polyelectrolytes ; polyampholytes ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In connection with our work on polyelectrolyte complex formation with polyampholytes, the interaction between invertase and several linear polyelectorlytes has been investigated by means of turbidimetry, light scattering measurements, and determination of the enzyme activity. Polyelectrolyte complex formation of invertase was shown to occur with cationic polyelectrolytes only. The light-scattering data yield information on aggregation and desegregation processes in complex formation. As indicated by our results, only a part of the protein molecules is engaged in this Coulombic interaction, and this part shows a rather small enzyme activity only. Thus, a direct interaction between invertase and a cationic polyelectrolyte is no effective approach to enzyme binding, but a complete immobilization of invertase can be achieved via an “inclusion flocculation” with a symplex formed by interaction between an anionic and a cationic linear polyelectrolyte or via immobilization in symplex microcapsules.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380909
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  • 59
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    Utility of culture redox potential for identifying metabolic state changes in Amino acid fermentation (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1034-1040 
    Details
    ISSN: 0006-3592
    Keywords: amino acid fermentation ; culture redox potential ; fermentation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: We investigated the relationship of dissolved oxygen and culture redox potential (CRP) on amino acid production. Corynebacterium glutamicum ATCC 14296 was used for all experiments. The fermentation can be divided into a growth phase and a production phase. Our results indicate that in order to get higher amino acid production, a lower oxygen supply during the exponential phase is favored. A higher oxygen supply rate appears to be necessary during the production phase. Culture redox potential (CRP) was used to monitor the fermentation. CRP readings were observed to drop to a characteristic minimum value as the metabolic state changed from a growth to production phase. This was evidenced by the commencement of amino acid production and a simultaneous uptake of lactate. Upon lactate exhaustion, the CRP increased abruptly. At the same time, maximal amino acid yields were observed. By the use of minimum CRP as an indication of metabolic phase changes, the agitation rate was changed to increase oxygen supply during the production phase. This significantly increased amino acid production. These results show that culture redox potential measurements can be used to monitor and optimize amino acid production by process manipulation.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380912
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  • 60
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    Simple structured model for α-amylase synthesis by Bacillus amyloliquefaciens (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1065-1081 
    Details
    ISSN: 0006-3592
    Keywords: mRNA ; transcription ; translation ; excretion ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A predictive, simple, structured model describing the synthesis of α-amylase by Bacillus amyloliquefaciens was formulated. Three key intracellular processes were identified (i.e, translation, and excretion) along with two key intracellular components (i.e., mRNA and the intracellular form of the α-amylase enzyme). Nearly all the model parameters were estimated by means of performing independent experiments, primarily fed-batch experiments. The model was shown to predict transient system behavior in batch and in fed-batch operation with some limitation and minor model parameter revisions. Since a principal objective was to demonstrate that independent experimental parameter determination can be used to construct the predictive model, further fine-tuning of the parameters may be necessary before application for optimization and control purposes.
    Additional Material: 17 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380916
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  • 61
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    Expression of recombinant protein A from the lac promoter in Escherichia coli JM83 is not subject to catabolite repression when grown under specific conditions of continuous culture (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1050-1058 
    Details
    ISSN: 0006-3592
    Keywords: catabolite repression ; protein A ; membrane proteins ; continuous culture ; protein expression ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Although widely used in experimental and industrial situations, genetically engineered plasmids containing the lac promoter from Escherichia coli are subject to catabolite repression when grown in glucose-containing media. Several methods of overcoming this problem have been investigated by studying the expression of the protein A gene from Staphylococcus aureus under the control of the Escherichia coli lac promoter. When glycerol is used as a sole carbon source, the plasmid is unstable and is rapidly lost from the culture. When the bacteria are grown in chemostats under glucose limitation, the plasmid is maintained, even at high dilution rates, and the expression of protein A is similar to that observed when glycerol was used. The balance between metabolic load and protein A expression seems to be maintained by reducing the gene dose to a tolerable level. Depending on the metabolic conditions prevailing in the culture, this is achieved, either by reducing the copy number of the plasmid or in extreme cases by removing the plasmid altogether.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380914
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  • 62
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    Assessment of virus production and chloramphenicol acetyl transferase expression by insect cells in serum-free and serum-supplemented media using a temperature-sensitive baculovirus (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1091-1099 
    Details
    ISSN: 0006-3592
    Keywords: chloramphenicol acetyl transferase ; baculovirus ; Spodoptera frugiperda ; serum-free medium ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Spodoptera frugiperda insect cells were grown in Sf-900 serum-free medium and two kinds of serum-supplemented media (IPL -41 and Grace's). The specific growth rates of uninfected cells were found to be 0.024, 0.35, and 0.034 h-1 respectively, at 33°C. The IPL -41 medium supported to highest maximum cell density (10.6 × 106 cells/mL) compared to 3.5 × 106 and 8.7 × 106 cells/mL with the Grace's and serum-free media, respectively. In temperature shifdown experiments with a temperature-sensitive baculo-virus (acts10YM1CAT), virus titer and chloramphenicol acetyl transferase (CAT) expression were highest in the IPL -41 (5.1 × 107 PFU/mL and 20000 U/mL). Use of Grace's medium gave higher virus titers than the serum-free medium (4.4 × 106 vs 4.1 × 105 PFU/mL) as well as higher CAT titers (7050 vs 1980 U/mL). Interestingly, in the three media used, the highest virus and CAT titers were obtained at MOI (multiplicity of infection) of 0.02 At MOI of 2.0 virtually no increase in virus of CAT titer was observed. This result is contrary to those obtained at constant-temperature (27°C) infection and cell culture, in which higher virus titers and recombinant protein expression and obtained at higher MOI.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380918
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  • 63
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    Catalytic action of L-2-halo acid dehalogenase on long-chain L-2-haloalkanoic acids in organic solvents (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1114-1117 
    Details
    ISSN: 0006-3592
    Keywords: L-2-halo acid dehalogenase ; dehalogenation ; in dimethyl sulfoxide ; 2-hydroxy acids ; stereospecific production of substrate specificity ; change in organic solvent ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A Lyophilized preparation of L-2-halo acid dehalogenase was not only stable but also catalytically active in anhydrous dimethyl sulfoxide, toluene, and other organic solvents. 2-Halo acids with long alkyl (C5-C16) or aromatic (phenyl and benzyl) side chains were inert in water but dehalogenated effectively in anhydrous dimethyl sulfoxide by the lyophilized enzyme. Long chain 2-haloalkanoic acids such as 2-bromohexadecanoic acids were better as substrate than short-chain halo acids (e.g., 2-chloropropanoic acid). The dehalogenation proceed with inversion of C2 configuration to produce the corresponding (2R)-2-hydroxy acids in anhydrous dimethyl sulfoxide in the same way as found in water.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380921
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  • 64
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    Solvent effects on biocatalysis in organic systems: Equilibrium position and rates of lipase catalyzed esterification (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1137-1143 
    Details
    ISSN: 0006-3592
    Keywords: organic-phase biocatalysis ; equillibrium ; reaction rates ; log P ; solvent choice ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Porcine pancreatic lipase immobilized on celite particles has been employed as a catalyst for the esterification of dodecanol and decanoic acid in a predominantly organic system. Solvent influence on the equilibrium position and on the catalyst activity has been studied using 20 solvents, including aliphatic and aromatic hydrocarbons, ethers, ketones, nitro- and halogenated hydrocarbons, and esters. The equilibrium constant for esterification correlates well with the solubility of water in the organic solvent, which in turn shows a good relationship with a function of Guttman's donor number and the electron pair acceptance index number of the solvent. This may be rationalized in terms of the requirements for solvation of water and of the reactants. The catalyst activity, measured as the initial rate of the esterification reaction, is best correlated as a function of both n-octanol-water partition coefficient (log P) and either the electron pair acceptance index or the polarizability.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260381004
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  • 65
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    Continuous glycerolysis of olive oil by Chromobacterium viscosum lipase immobilized in liposome in reversed micelles (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1159-1165 
    Details
    ISSN: 0006-3592
    Keywords: continuous glycerolysis ; lipase adsorbed on liposome ; microemulsion ; reversed micelles ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Chromobacterium viscosum lipase which has adsorbed on liposome and solubilized in microemulsion droplets of glycerol containing a little amount of water could catalyze the glycerolysis of olive oil. Studies on the continuous glycerolysis of olive oil by the immobilized enzyme was done at 37°C in continuous stirred vessel bioreactor with polysulfone membrane. The effect of the flow rate of substrate (olive oil) in isooctane on the conversion and composition of the outlet was investigated using high-performance liquid chromatography (HPLC). The conversion increased with decrease in the flow rate. And we studied the effect of water content in the glycerol-water-lipase solution on the glycerolysis reaction. The conversion to desirable products, mono- and di-olein, was improved without a substantial production of oleic acid at lower water concentrations, i.e., below 8.0% (w/v) which corresponds to a wo value of 0.97. At water concentration higher than 8.0% (w/v), the amount of free fatty acid was dramatically increased. Higher operational stability of the enzyme reactor, and the half-line of the enzyme continuous reaction was about 7 weeks.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260381007
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  • 66
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    High-density photoautotrophic algal cultures: Design, construction, and operation of a novel photobioreactor system (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1182-1189 
    Details
    ISSN: 0006-3592
    Keywords: photobioreactor ; ultrfiltration ; photoautotrophic ; DNA histograms ; cell cycle ; flow cytometry ; chlorella vulgaris ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A photobioreactor system has been designed, constructed and implemented to achieve high photosynthetic rates in high-density photoautotrophic algal cell suspensions. This unit is designed for efficient oxygen and biomass production rates, and it also can be used for the production of secreted products. A fiber-optic based optical transmission system that is coupled to an internal light distribution system illuminates the culture volume uniformly, at light intensities of 1.7 mW/cm2 over a specific surface area of 3.2 cm2/cm3. Uniform light distribution is achieved throughout the reactor without interfering with the flow pattern required to keep the cells in suspension. An on-line ultrafiltration unit exchanges spent with fresh medium, and its use results in very high cell densities, up to 109 cells/mL [3% (w/v)] for eukaryotic green alga chlorella vulgaris. DNA histograms obtained form flow cytometric analysis reveal that on-line ultrafiltration influences the growth pattern. Prior to ultrafiltration the cells seem to have at a particular point in the cell cycle where they contain multiple chromosomal equivalents. Following ultrafiltration, these cells divide, and the new cells are committed to division so that cell growth resumes. The Prototype photobioreactor system was operated both in batch and in continuous mode for over 2 months. The measured oxygen production rate of 4-6 mmol/L culture h under continuous operation is consistent with the predicted performance of the unit for the provided light intensity.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260381010
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    Steroid bioconversion in a microemulsion system (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1210-1217 
    Details
    ISSN: 0006-3592
    Keywords: Δ1,2-dehydrogenation of high steroid concentrations ; microemulsion system ; enzyme kinetics ; biphasic system ; stability in ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The Δ1,2-dehydrogenation of high concentrations of the steroid -methyl-Reichstein's compound S-21-acetate (16MRSA) in a microemulsion system was studied using heat-dried and thawed Arthrobacter simplex cells as biocatalyst. The microemulsion system consists of an organic phase [75-95% (v/v)] with steroid (1-60 g/Ltot), an aqueous phase [5-25% (v/v)] containing the cells (5-30 g/Ltot), and a neutral surfactant (5-20 g/L organic solvent). Benzene derivatives, which solubilize 16MRSA up to 94 g/L, and phospholipids were used as organic solvents and surfactants, respectively, and menadione was added as an external electron acceptor. Factors affecting the dehydrogenation rate in the microemulsion system were studied. The influences of the 16MRSA and the menadione concentration on the dehydrogenation rate were described by Michaelis-Menten kinetics, apparent V′max and K′m values of 2.06 g/g dry weight h and 18.9 g/L for 16MRSA and 4.97 g/g dry weight h and 1.91 g/L for menadione being obtained. Optimal menadione concentration was dependent on the steroid concentration was dependent on the steroid concentration used. The reaction was strongly inhibited by high product concentrations. Much higher activities were obtained with the thawed cells than with the dried cells, conversions of 98% being reached within 14-16 h. for 16MRSA and cell dry weight concentrations of 40 and 10 g/L, respectively. Activity retention in a batch stirred tank reactor remained constant during the first 16-24 h of operation and then decreased, depending on the stirring rate; 22 to 65% of the initial reaction rate was obtained after 48 h at stirring rates of 650 and 2000 rpm, respectively.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260381013
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  • 68
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    Production of emulsan in a fermentation process using soybean oil (SBO) in a carbon-nitrogen coordinated feed (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1259-1259 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260381020
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  • 69
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    Masthead (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991) 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260381101
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  • 70
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    Studies of the reductive biotransformation of selected carbonyl compounds by whole cells and extracts of baker's yeast, Saccharomyces carevisiae (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1280-1284 
    Details
    ISSN: 0006-3592
    Keywords: Saccharomyces cerevisiae ; biotransformation ; oxidoreductases ; carbonyl ; stereospecific ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The progress of reductive biotransformations of a variety of earbonyl compounds by whole cells of baker's yeast was monitored with time. Biotransformations rates ranged from 0.11 to 112.12 mg product formed per g dry yeast per h. While rapid biotransformations of citronellal and ethyl benzoylformate were observed, complete conversion of substrate to product did not occur. Reductive conversions of ethyl- and methyl-acetoacetate went to completion in 6 and 12 h respectively. Ethyl mandelate was produced stereoselectively, favoring the (R)- stereoisomer and ethyl and methyl-3-hydroxybutyrate were produced with (S)-enantiospecificity. Yeast crude extract and resuspended presence of NAD(P)H. Ethyl benzoylformate and methyl-and ethyl-acetoacetate were preferentially reduced by yeast crude extract as compared to resuspended pellet and, in the case of the former two substrates, the reaction manifested a preference for NADPH over NADH.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260381104
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    Selective separation and purification of two lipases from chromobacterium viscosum using AOT reversed micelles (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1302-1307 
    Details
    ISSN: 0006-3592
    Keywords: liquid-liquid extraction ; selective separation of proteins ; reversed micelles ; purification ; lipases ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Selective separation and purification of two lipases form Chromobacterium viscosum were carried out by liquid-liquid extraction using a reversed micellar system. Optimum parameters for extraction were determined using a 250 mM AOT micellar solution in isooctane. Complete separation of the two lipases was achieved at pH 6.0 with a 50mM potassium phosphate buffer solution containing 50 mM KCI. By adding 2.5% by volume of ethanol to the lipase-loaded micellar solution, 85% of the extracted lipase could be recovered in a new aqueous phase, 50 mM K2HPO4 with 50 mM KCl, at pH 9.0. Lipase A was purified 2.6-fold with a recovery of 86%, and lipase B by 1.5-fold with a recovery of 76%.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260381107
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    Biomass axial distribution in airlift bioreactor with yeast and plant cells (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1325-1330 
    Details
    ISSN: 0006-3592
    Keywords: biomass distribution ; bioreactor, loop airlift ; Saccharomyces cerevisiae ; Phaseolus vulgaris ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This study was aimed at determining the degree of biomass homogeneity in the various parts of an internal loop airlift bioreactor, thus verifying the assumption, often made in bioreactor studies, of a well-mixed liquid-biomass system. Following characterization of the hydrodynamics of the vessel with water, the axial biomass distribution in the riser and downcomer was determined for plant and yeast cell suspensions of 5.8, 8.5, and 12.5 g DW/L Phaseolus vulgaris and of 30 and 46 g DW/L Saccharomyces cerevisiae. The airlift bioreactor with a surface ratio AD/AD of 1.04 and aspect ratio of 4.95 was investigated under various aeration rates. The yeast cells were found to be distributed practically uniformly throughout the vessel at the aeration rates of 0.1-1.45 vvm. However, in the case of the denser and cluster-forming plant cells, a clear trend of a gradual bio-mass accumulation in the downcomer, a slightly lower but uniform biomass loading in the riser, and a slightly higher biomass concentration in the gas-liquid separator was observed at the lower aeration rates of 0.1-0.61 vvm. In the case of powderized calcium carbonate (55g/L) often used in fermentations of organic acids, a slight trend of a gradual accumulation of solids towards the bottom parts in both the downcomer and riser was observed. A better representative sampling location, in terms of solids and biomass loading, seems to be in the middle part of the vessel. It is suggested that airlift bioreactors with higher aspect ratios (〉5) may be prone to a more significant inhomogeneity of solids (biomass and particles).
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260381110
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    Rapid determination of plasmid-carrying yeast cells by using an imaging sensor system (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1331-1336 
    Details
    ISSN: 0006-3592
    Keywords: plasmid ; yeast ; detection ; sensor ; image ; analysis ; 5-fluoro-orotic acid ; determination ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A novel imaging sensor system for the determination of plasmid carrying yeast cells was developed. The sensor system consisted of an Silicon Intensifier Target (SIT) video camera, a fluorescent microscope, and a personal computer system equipped with an image memory board. This system was based on the fact that the membrane integrity of only plasmid-carrying cells is lost following cell growth in 5-fluoro-orotic acid (5-FOA) containing medium, and consequently these target cell can be stained with fluorescent probes and detected. In this study, plasmid-carrying cells were detected and their fraction determined in a mixture of both plasmid-carring and plasmid-free cells. A good correlation was observed between the values determined by this sensor system and the conventional method in the 30%-80% range, and one assay was possible within 4 h. This sensor system could be used for the monitoring of plasmid-carrying fraction in recombinant yeast cells during cultivation.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260381111
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    Uptake of cadmium and zinc by the alga Chlorella vulgaris: II. Multi-ion situation (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 445-455 
    Details
    ISSN: 0006-3592
    Keywords: synergism antagonism ; metal uptake ; Chlorella vulgaris ; cadmium ; zinc ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Many microorganisms are capable of sequestering and concentrating heavy metals from their aqueous environment. While much research has beep carried out on the uptake of single species of metal ions, little attention seems to have been given to the study of multimetal ion systems. A mathematical model has previously been developed to describe the uptake of individual metal species by a microorganism. The model proposes two sequential processes: an initial rapid uptake due to cellular surface adsorption and a subsequent slow uptake due to membrane transport of the metal into the cells. This article extends the treatment by considering the uptake of two metal species together, cadmium and zinc, under different experimental conditions. The results are discussed in terms of possible mechanistic interactions.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260370506
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  • 75
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    A novel magnetic silica support for use in chromatographic and enzymatic bioprocessing (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 614-626 
    Details
    ISSN: 0006-3592
    Keywords: chromatography ; immobilized enzyme ; magnetically stabilized fluidized bed ; silica ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A limited number of support matrices have so far been developed for use in magnetically stabilized fluidized bed (MSFB) applications. We have developed a versatile magnetic silica support which can be derivatized readily for both adsorption chromatography and enzyme immobilization by well-known techniques. A magnetic pellicular bead is prepared by electrostatically depositing alternating layers of colloidal silica and cationic polymer onto macroscopic nickel core particles. The polymer is then burned out and the silica partially sintered to yield a porous shell with 5-80 m2/g of surface area. This magnetic composite was tested as a support for immobilizing invertase. Sucrose was continuously converted to its component monosaccharides with nearly constant activity over the first 8 days and retention of 50% of initial activity after 25 days.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260370704
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    Measurement of bacterial random motility and chemotaxis coefficients: II. Application of single-cell-based mathematical model (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 661-672 
    Details
    ISSN: 0006-3592
    Keywords: bacterial chemotaxis ; Escherichia coli ; random motility ; diffusion chamber assay ; mathematical model ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A quantitative description of bacterial chemotaxis is necessary for making predictions about the migratory behavior of bacterial populations in applications such as biofilm development, release of genetically engineered bacteria into the environment, and in situ bioremediation technologies. The bacterial chemotactic response is characterized by a mathematical model which relates individual cell properties such as swimming speed and tumbling frequency to population parameters, specifically the random motility coefficient and the chemotactic sensitivity coefficient. Our model includes a nonlinear dependence of the chemotactic velocity on the attractant gradient as well as a dependence of the random motility coefficient on the temporal and spatial attractant gradients, both of which previous analyses have neglected. As we will show, these aspects are critical for interpreting the results from experiments like those performed in the stopped-flow diffusion chamber (SFDC) because the initial temporal and spatial gradients are very steep. Our analysis demonstrates that values for the random motility coefficient and chemotactic sensitivity coefficient can be obtained from experimental plots of net cell redistribution from initial conditions versus the square root of time. Values for these parameters are determined from experimental measurements of bacterial population distributions in the SFDC as described in the companion article. Using parameter values determined from independent experiments, μ = 1.1 ± 0.4 ± 10-5 cm2/s and χ0 = 8 ± 3 ± 10-5 cm2/s, excellent agreement is found between theoretically predicted bacterial density profiles and actual experimental profiles for Escherichia coli K12 responding to fucose over two orders of magnitude in initial attractant concentration. Thus, our model captures the concentration dependence of this behavioral response satisfactorily in terms of cell population parameters which are derived from individual cell properties and will therefore be useful for making predictions about the migratory behavior of bacterial populations in the environment.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260370708
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    Masthead (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991) 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260370801
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  • 78
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    The production of the enzyme dextransucrase using nonaerated fermentation techniques (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 703-707 
    Details
    ISSN: 0006-3592
    Keywords: Dextransucrase ; Leuconostoc mesenteroides ; fermentation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: High yields of the enzyme dextransucrase have been produced repeatedly by fed-batch fermentation techniques. Activities in excess of 21.9 U/cm3 have been obtained by culturing Leuconostoc mesenteroides NRRL B-512(F) under nonaerated fed-batch fermentation conditions. Aerobic fermentations carried out under identical conditions have consistently produced enzyme of less than 17 U/cm3, but with no difference in the final cell concentration in the broth. Different types of yeast extract have been found to have significant effect on the final cell concentration and more especially on the enzyme activity with enzyme yields varying by as much as 50% when different types of yeast extracts were used.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260370803
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  • 79
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    Batch fermentation kinetics of sugar beet molasses by Zymomonas mobilis (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 304-313 
    Details
    ISSN: 0006-3592
    Keywords: Zymomonas mobilis ; molasses ; fermentation ; ethanol ; osmolality ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A new osmotolerant mutant strain of Zymomonas mobilis was successfully used for ethanol production from beet molasses. Addition of magnesium sulfate to hydrolyzed molasses allowed repeated growth without the need of yeast extract addition. The kinetics and yields parameters of fermentation on media with different molasses concentrations were calculated. The anabolic parameters (specific growth rate, μ, and biomass yield, YX/S) were inhibited at elevated molasses concentrations while the catabolic parameters (specific ethanol productivity, qp, and ethanol yield, Yp/s) were not significantly affected. In addition to ethanol and substrate inhibition, osmotic pressure effects can explain the observed results.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380312
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  • 80
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    Protease-catalyzed peptide synthesis using inverse substrates: The synthesis of Pro-Xaa-bonds by trypsin (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 319-321 
    Details
    ISSN: 0006-3592
    Keywords: Protease ; acyl transfer ; nucleophile efficiency ; inverse substrates ; trypsin ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Benzyloxycarbonyl-L-proline p-guanidinophenyl ester is an “inverse substrate” for trypsin; i.e., the cationic center is included in the leaving group instead of being in the acyl moiety. This substrate can be used in trypsin-catalyzed acyl-transfer reactions leading to the synthesis of Pro-Xaa peptide bonds. The reaction proceeds about 20 times slower than reaction with similar alanine-containing substrates, but the ratio between synthesis and hydrolysis is more favorable. The investigation of a series of nucleophiles led to information about the specificity of the process. Nucleophiles differing only in the P1′-position show an increasing acyl transfer efficiency in the order Phe 〈 Gly 〈 Ley 〈 Ser 〈 Ala 〈 lle. C terminal elongation of the nucleophiles is of minor influence on their efficiency. The formation of an H bond between the acyl-enzyme and the nucleophile seems to play an important role in the aminolysis of the acyl-enzyme.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380314
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  • 81
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    Critical assessment of gassing-in methods for measuring kla in fermentors (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 323-330 
    Details
    ISSN: 0006-3592
    Keywords: oxygen transfer ; oxygen-enriched air ; dynamic pressure method ; steady-state feeding method ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The reliability of dynamic measurement methods of kla in fermentors using a step oxygen concentration change in the feed gas was tested. The tests were performed both for the original variant using the nitrogen ⇌ air exchange and the newly presented variant using the oxygen-enriched air (27 vol % O2) → air exchange. The testing consisted in comparing kla values determined from these methods with values determined from the steady-state Na2SO3 feeding method and the dynamic pressure method, the reliability of which was proven earlier. The measurements were done in water (coalescent batch) and in 0.5M Na2SO4 solution with and without the addition of 1 wt % carboxymethylcellulose (noncoalescent batches). It was found that in noncoalescent liquids the methods tested give extremely low kla values (as low as 15% of the correct value). The methods are defective in principle irrespective of the gases used for exchange.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380402
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    A semimechanistic mathematical model for growth of Rhizopus oligosporus in a model solid-state fermentation system (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 353-362 
    Details
    ISSN: 0006-3592
    Keywords: Rhizopus oligosporus ; fermentation ; starch ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A Semimechanistic mathematical model is developed which describes the growth of Rhizopus oligosporus in a model solid-state fermentation system. Equations are presented for the release of glucoamylase, the diffusion of glucoamylase, the hydrolysis of starch, the generation and diffusion of glucose, and the uptake of glucose and conversion into new biomass. Good agreement of the model with the experimental data was obtained only after the glucoamylase diffusivity and the maximum specific glucose uptake rate were altered from their originally determined values. The model recognizes the distributed nature of the solid-state fermentation and therefore is able to predict the concentration profiles of the system components within the substrate. The model provides an insight into the possible rate-limiting steps in solid-state fermentation - the generation of glucose within the substrate and the resulting availability of glucose at the surface.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380405
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  • 83
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    Effects of Glutamate, Glucose, Phosphate, and Alkali metal ions on cephamycin C production by Nocardia lactamdurans in defined media (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1100-1109 
    Details
    ISSN: 0006-3592
    Keywords: cephamycin ; Nocardia lactamdurans ; nutrient regulation ; antibiotic fermentation ; nitrogen metabolism ; phosphate limitation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A High cephamycin C producing strain of Nocardia lactam-durans was used to study cell growth and antibiotics production in defined media. Batch fermentations in shake flasks and stirred tanks showed that antibiotic production occurred during cell growth and the production rate rapidly decline as the growth slowed. Glutamate served as a primary substrate during this phase. Later, ammonia was utilized along with a remainder of the glucose. Rapid antibiotic production occurred in this phase. Increased glutamate promoted higher growth, a rise in ammonium ion concentration, and a marked reduction in antibiotic titers. An increase of the glucose concentration along with the glutamate concentration balanced to the medium; no ammonium ion rise occurred and a peak specific antibiotic titer comparable to the control medium was obtained. In a phosphate-limited medium, cell growth equivalent to the control medium and increased antibiotic titers were obtained. In these experiments, adjustment of Na+ and K+ ion concentration equal to that in the control medium was found to be important. Based on carbon and nitrogen balances, the activity of the key nitrogen metabolism enzymes, and the published literature, a two-stage model of regulation is suggested.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380919
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    Protein extraction by reverse micelles: A study of the factors affecting the forward and backward transfer of α-chymotrypsin and its activity (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1239-1246 
    Details
    ISSN: 0006-3592
    Keywords: protein extraction ; α-chymotrypsin ; micelles ; reverse ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: α-chymotrypsin is taken as a model protein to investigate three aspects of the protein extraction by reverse micelles: (1) the comparison between the two forward transfer techniques, i.e., the liquid-liquid and the solid state-liquid transfer; (2)the back-transfer, i.e., the capability of the protein to be recovered from the micellar solution; and (3) the maintainance of the enzyme activity at the end of the extraction cycle. Concerning the forward transfer from the liquid phase, we study first the effect of salt initially present in the aqueous phase on the equilibrium concentration of the extracted species; further, we study the forward protein extraction from the solid state, and the effect of pH, salt, and protein concentration on the transfer efficiency. Concerning the back transfer, we find the somewhat surprising result, that the percentage of protein back-extraction depends on the type and concentration of salt used for the forward transfer. Preliminary data concerning an alternative method for the back-transfer using silica gel to liberate the protein from the micellar environment, are presented. Finally, it is found that the enzyme activity depends again on the type and concentration of salt used for the forward transfer.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260381017
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  • 85
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    Growth and immobilization of tripterygium wilfordii cultured cells (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1285-1291 
    Details
    ISSN: 0006-3592
    Keywords: Tripterygium Wilfordii ; plant cell culture ; suspension ; medium ; immobilization ; bioreactor culture ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The plant Tripterygium wilfordii produces di- and triterpenes of interest for male contraception and treatment of arthritis and skin disorders. Cell line TRP4a obtained form this plant in 1981 was reported to produce these valuable compounds at yields (∼0.04% of the biomass dry weight) higher than found in the plant (0.001%). In order to improve this production, studies were carried out to determine the feasibility of eliminating the troublesome component of coconut milk originally used to culture this cell line. A defined formulation suitable for growth ad maintenance has been developed. This medium consisted of Gamborg's PRL4 or B5 medium supplemented with 2 mg L-1 2,4-dichlorophenoxyacetic acid and 20 g L-1 sucrose. Furthermore, monitoring of carbohydrate uptake revealed that T. wilfordii cells, contrary to many plant cell species, did not hydrolyze sucrose extra-cellularly before uptake. Replacement of this disaccharide by glucose or fructose increased specific growth rate from 0.15 to 0.25 day-1. As tripdiolide is reported to be present in broth extract in significant amounts, plant cell immobilization technology offers a promising alternative to suspension cultures, especially in view to on line harvesting of the product. Surface immobilized T. wilfordii cell cultures were successfully carried out in 2-L bioreactors. Their biomass production and carbohydrate uptake were comparable to those observed for shake flask grown suspension cultures. Higher nitrate and ammonium uptake were found in immobilized cultures.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260381105
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  • 86
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    Saccharification of steam-exploded poplar wood (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1308-1317 
    Details
    ISSN: 0006-3592
    Keywords: Trichoderma reesei CL-847 ; steam explosion treatment ; saccharification ; inactivation ; cellulose ; hemicelluloses ; lignin ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Effects of time, temperature, and pH during the steam explosion of poplar wood were studied with the aim of optimize both pentoses recovery and enzymatic hydrolysis efficiency. Steam explosion of acid impregnated wood chips allowed the recovery of 70% of potential xylose as monomers (217°C, 120 s) Enzymatic hydrolysis of pretreated fiber with Trichoderma reesei CL-847 cellulase system increased progressively with the severity of the steam treatment conditions. The best yield in term of glucose recovery after 24 h of enzymatic hydrolysis was 70% of potential glucose (225°C, 120 s). Deactivation by adsorption on lignin of Trichoderma reesei cellulases and inhibition of these enzymes by low-molecular-weight phenols and trihydroxybutyric acids were noticed.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260381108
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  • 87
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    Metabolic regulation in bacterial continuous cultures: I (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1337-1352 
    Details
    ISSN: 0006-3592
    Keywords: Klebsiella pneumoniae ; metabolic regulation ; continuous cultures ; cybernetic model ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Dilution rate steps in continuous culture experiments with Klebsiella pneumoniae growing on single substrate feeds have brought out interesting features of metabolic regulation not observed in batch cultures. In a step-up experiment, the adjustment of the culture to a new steady state is preceded by an undershoot in cell density. Results of a step-down experiment indicate a corresponding overshoot phenomenon. These observations of the transient behavior of the culture growing on glucose and xylose as well as the steady-state results are interpreted with cybernetic models. The development of the model explicitly accounts for the lumped internal resource, which is optimally allocated toward the synthesis of key enzymes catalyzing different cellular processes. The model also includes a description of the increased maintenance demand observed at low growth rates. It reduces to previous cybernetic models in situations where the cell does not experience a sudden change in its environment and, hence, retains their predictive capability.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260381112
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    Comments on a segregated model of recombinant cultures: Authors' reply (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1364-1365 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260381114
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  • 89
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    Performance of the anaerobic baffled reactor under steady-state and shock loading conditions (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 344-355 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The anaerobic baffled reactor (ABR) contains a granulated, mixed anaerobic culture segregated into compartments. Operation of four reactors under a range of hydraulic retention times showed that this novel reactor design offers highly efficient performance in the conversion of carbon in the feed stream to methane and carbon dioxide. The design parameter varied was the number of compartments. COD removal at 20 h retention time was routinely over 95% in all reactors, with low washout of biomass. Very high specific reaction rates were achievable (although with a loss of efficiency) at low biomass concentrations and high loading rates. In order to optimize volumetric reaction rates, a tradeoff has to be made between high biomass concentration, granule size, and the resulting mass transfer limitations. Formate is shown to be an important intermediate in the process under conditions of high loading.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260370408
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  • 90
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    Effect of agitational shear on growth and protease production by Thermomonospora fusca (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 371-374 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260370411
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  • 91
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    Transient response method for evaluating the rate constants of reactions over immobilized enzymes (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 922-926 
    Details
    ISSN: 0006-3592
    Keywords: transient response method ; rate constants ; immobilized enzyme ; glucose oxidation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The transient response method was utilized to evaluate the rate constants of reaction over immobilized enzyme. Glucose oxidation catalyzed by the immobilized glucose oxidase in a fixed-bed reactor was selected as an example. A theoretical model including the effects of axial dispersion, film diffusion, and intraparticle diffusion was established for the reactor. The individual rate constant of each elementary step of this enzymatic reaction was determined through direct fitting of the experimental response data to the model.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260371005
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  • 92
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    Semicontinuous enzymatic hydrolysis of lignocelluloses (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 948-954 
    Details
    ISSN: 0006-3592
    Keywords: cellulase ; cellulose hydrolysis ; steam treatment ; ultrafiltration ; enzyme adsorption ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Lignocelluloses (steamed hardwood and hardwood kraft pulp) were semicontinuously hydrolyzed on a large scale [2-2. 5 kg of substrate vs. 20, 000 IU filter paperase (FPase)] using a 10-L hydrolysis reactor with an ultrafiltration unit for the recovery and reuse of cellulases. The substrate was added to the reactor at appropriate intervals to keep a concentration of approximately 5% (w/v). All of the enzyme was added at the beginning and no further addition was done. The ultrafiltration unit was operated intermittently rather than continuously due to its enough capacity (dilution rate of 2.5 h-1) and making the enzyme durable. The enzyme required to produce one gram of reducing sugar in this reactor was 27.3 FPase IU/g RS for steamed hardwood and 7.4 FPase IU/g RS for hardwood kraft pulp. The sugar composition of hydrolyzate was unaltered virtually from beginning to end of the hydrolysis in spite of the progressive loss of enzyme activities. The analysis of the enzyme composition in the hydrolyzate during hydrolysis revealed that an exo-β-D-glucanase component was adsorbed selectively at the stages of advanced hydrolysis extent.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260371008
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  • 93
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    Mass production of human epidermal growth factor using fed-batch cultures of recombinant Escherichia coli (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 37-42 
    Details
    ISSN: 0006-3592
    Keywords: Escherichia coli ; growth factor ; epidermal growth factor ; fed batch culture ; human epidermal growth factor ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Fed-batch cultures of recombinant E. coli HB101 harboring expression plasmid pTRLBT1 or pTREBT1, with acetate concentration monitoring, are investigated to obtain high cell density and large amounts of human epidermal growth factor (hEGF). The expression plasmid pTRlBT1 contains a synthetic hEGF gene attached downstream of the N-terminal fragment of the trp L gene preceded by the trp promoter. The expression plasmid pTREBT1 contains the same coding sequence attached downstream of the N-terminal fragment of the trp E gene preceded by the trp promoter, trp L gene, and attenuator region. E. coli harboring pTREBT1 produces 0.56 mg/L hEGE and immediately degrades it. On the other hand E. coli harboring pTRLBT1 produces 6.8 mg/L hEGF and does not decompose it. Prominent inclusion bodies are observed in E. coli cells harboring pTRLBT1 using an election microscope. To Cultivate E. coli harboring pTRLBT1, a fed-batch culture system, divided into a cell growth step and an hEGF production step, is carried out. The cells grow smoothly without acetate-induced inhibition. Cell concentration and hEGF quantity reach the high values of 21 g/L and 60 mg/L, respectively.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380106
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  • 94
    Electronic Resource
    Electronic Resource
    Cleaning of inorganic membranes after whey and milk ultrafiltration (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 82-89 
    Details
    ISSN: 0006-3592
    Keywords: cleaning membrane ; fouling ; UF membrane ; milk ; whey ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Cleaning of an inorganic ultrafiltration membrane has been quantified through hydraulic, physicochemical, and spectroscopic (infrared and x-photoelectron spectroscopy) analyses. An efficient cleaning sequence of nitric acid followed by sodium hypochlorite has been proposed for cleaning of defatted whey protein concentrate and milk ultrafiltration membranes. The influence of reversed sequence and time reduction are discussed together with the action of both cleaning chemicals. In spite of residual fouling left after every cleaning sequence studied, hydraulic cleanliness of the membrane was achieved, particularly after the standard procedure.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380111
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  • 95
    Electronic Resource
    Electronic Resource
    Enzymic hydrolysis of lignocellulosic materials: I. Models for the hydrolysis process  -  a theoretical study (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 135-138 
    Details
    ISSN: 0006-3592
    Keywords: enzymic hydrolysis ; enzyme recovery ; process models ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: At the end of an enzymic hydrolysis process involving a solid lignocellulosic substrate, enzymes are found both in solution and absorbed to the substrate residue. Removal of residue from the system will result in loss of some of the enzymes, the extent of which will depend on the design of the process. To minimize enzyme loss, a study has been conducted in which six process models have been formulated and an enzyme loss function derived for each model based on the total amount of enzymes lost through residue removal. Model 1 is a reference model, characterized by an uninterrupted hydrolysis throughout the entire hydrolysis period. The residue is then washed in order to recover both sugar and adsorbed enzymes before the residue is discarded. Models 2-6 are all characterized by the removal of hydrolysate three times during the process, recirculation of dissolved and adsorbed enzymes to various points in the process and selection of a stage at which the residue is removed. The following conclusions could be drawn from the derived enzyme loss functions: Increased enzyme adsorption leads to increased enzyme loss.The enzyme loss decreases if the solid residue is removed late in the process.Both adsorbed and dissolved enzymes should be introduced at the starting point of the process. This is particularly important for dissolved enzymes. Three models were chosen for experimental studies, which are reported in a second, accompanying article. The experimental results obtained are compared with the theoretical study reported here.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380205
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  • 96
    Electronic Resource
    Electronic Resource
    Influence of the screen material on the fouling of spin filters (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 159-168 
    Details
    ISSN: 0006-3592
    Keywords: spin filter ; plugging ; fouling ; perfusion ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Mouse-mouse hybridomas (15 μm mean diameter) were cultivated in a simulated perfusion reactor with spin filter and external recirculation of the medium. Proteins at high concentrations, such as 10% foetal calf serum (FCS), were found to be not responsible by themselves for fouling, even at high recirculation rates. Stainless steel (10 μm pores) in contrast to polyamide (11 μm proes) led to a great accumulation of dead cells and nucleic acids on the screen, finally leading to fouling, as shown by biochemical and microscopic examinations. It is suggested that the high surface charge density of metals compared to polyamide is responsible for attachment of various residues. Stainless steel should rather be replaced by a resistant and nontoxic synthetic material, such as polyamide 66 which was successfully used. FCS should be avoided, since it seems to increased the fouling phenomenon. Moreover, the pore size of the screen should be carefully defined according to the wide size distribution of living and dead cells of the line used (33% of variation of the mean size in our case) as well as fragments. The purpose of the screen being to get rid of fragments and small dead cells, and not to wash too many new small cells, a good retention was achieved here by a 10-μm opening.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380208
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  • 97
    Electronic Resource
    Electronic Resource
    Measurement and regulation of the culture reduction state in Clostridium acetobutylicum (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 181-190 
    Details
    ISSN: 0006-3592
    Keywords: solventogenic metabolism ; NADH content ; NADH fluorescence ; continuous fermentation ; butanol biosynthesis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: With a constant glucose feed concentration, the change in the continuous culture dillution rate resulted in an altered fermentation profile and the cellular NADH content. The cultures growing at high dillution rates demonstrated an oxidative metabolism low NADH and butanol concentrations. The low specific NADH flourescence (F/X) at high butanol production rates suggested that a rapid regeneration of NADH to NAD is essential for a high solventogenic culture activity. The culture florescence and butanol concentration remained constant in the solventogenic dilution rate range of D = 0.05-0.2 h-1 with an inverse relationship between the specific flourescence (F/X) and the specific butanol production rate, qB. Flourometric NADH observations were confirmed by enzymatic NADH determination. The stiochiometric “Fermentation Equation” was used to check the experimental data consistency and to investigate the role of the available biosynthetic and reduction energy on the culture metabolic activities under different growth conditions. The butanol concentration in the broth was stabilized in a fed-batch process when the culture NADH fluorescence was being controlled through the addition of fresh medium.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380210
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  • 98
    Electronic Resource
    Electronic Resource
    Growth and substrate consumption of Nitrobacter agilis cells immobilized in carrageenan: Part 1. Dynamic modeling (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 224-231 
    Details
    ISSN: 0006-3592
    Keywords: modeling ; immobilized ; growth ; Nitrobacter ; sensitivity analysis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The modeling of the growth of Nitrobacter agilis cell immobilized in κ-carrageenan is presented. A detailed description is given of the modeling of internal diffusion and growth of cells in the support matrix in addition to external mass transfer resistance. The model predicts the substrate and biomass profiles in the support as well as the macroscopic oxygen consumption rate of the immobilized biocatalyst in time. The model is tested by experiments with continuously operated airlift loop reactors containing cells immobilized in κ-carrageenan. The model describes experimental data very well. It is clearly shown that external mass transfer may not be neglected. Furthermore, a sensitivity analysis of the parameters at their values during the experiments revealed that apart from the radius of the spheres and the substrate bulk concentration, the external mass transfer resistance coefficient is the most sensitive parameter for our case.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380303
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  • 99
    Electronic Resource
    Electronic Resource
    A model for light-limited continuous cultures: Growth, shading, and maintenance (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 254-259 
    Details
    ISSN: 0006-3592
    Keywords: light limitation ; shading ; maintenance ; mathematical model ; continuous culture ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Light-limited growth in continuous cultures of phototrophic organisms is modeled. It is assumed that light energy up-take rate depends hyperbolically on light intensity and that the maintenance costs are proportional to biomass. Modeling the light distribution caused by shading within the vessel is necessary to explain the existence of steady state in light-limited chemostats. The model fits well to experimental data from literature on light-limited chemostats and turbidostats. Attention is given to the implications of the model for the estimation of the specific maintenance rate constant in light-limited continuous cultures.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380307
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  • 100
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    Electronic Resource
    Parametric studies of ethanol production form xylose and other sugars by recombinant Escherichia coliFlorida Agricultural Experiment Station Publication Number R-01082. (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 296-303 
    Details
    ISSN: 0006-3592
    Keywords: ethanol ; genetic engineering ; Escherichia coli ; lignocellulose ; xylose ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The conversion of xylose to ethanol by recombinant Escherichia coli has been investigated in pH-controlled batch fermentations. Chemical and environmental parameters were varied to determine tolerance and to define optimal conditions. Relatively high concentrations of ethanol (56 g/L) were produced from xylose with excellent efficiencies. Volumetric productivities of up to 1.4 g ethanol/L h were obtained. Productivities, yields, and final ethanol concentrations achieved from xylose with recombinant E. coli exceeded the reported values with other organisms. In addition to xylose, all other sugar constituents of biomass (glucose, mannose, arabinose, and galactose) were efficiently converted to ethanol by recombinant E. coli. Unusually low inocula equivalent to 0.033 mg of dry cell weight/L were adequate for batch fermentations. The addition of small amounts of calcium, magnesium, and ferrous ions stimulated fermentation. The inhibitory effects of toxic compounds (salts, furfural, and acetate) which are present in hemicellulose hydrolysates were also examined.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380311
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