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  • 1985-1989  (560)
  • 1987  (560)
  • Biochemistry and Biotechnology  (560)
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987) 
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 1-12 
    ISSN: 0887-3585
    Keywords: protein crystallography ; protein refinement ; empirical energy simulations ; error analysis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The uncertainties in the refined parameters for a 1.5-Å X-ray structure of carbon-monoxy (FeII) myoglobin are estimated by combining energy minimization with least-squares refinement against the X-ray data. The energy minimization, done without reference to the X-ray data, provide perturbed structures which are used to restart conventional X-ray refinement. The resulting refined structures have the same, or better, R-factor and stereochemical parameters as the original X-ray structure, but deviate from it by 0.13 Å rms for the backbone atoms and 0.31 Å rms for the sidechain atoms. Atoms interacting with a disordered sidechain, Arg 45 CD3, are observed to have larger positional uncertainties. The uncertainty in the B-factors, within the isotropic harmonic motion approximation, is estimated to be 15%. The resulting X-ray structures are more consistent with the energy parameters used in simulations.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 13-19 
    ISSN: 0887-3585
    Keywords: two-dimensional electrophoresis ; ethylnitrosourea ; somatic mutations ; structural variants ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The feasibility of detecting human somatic structural gene mutations by two dimensional electrophoresis has been investigated. A lymphoblastoid cell line was grown as a mass culture in the presence of ethylnitrosourea, after which cells were regrown as single cell clones. A total of 257 polypeptide spots were analyzed in gels derived from 186 clones. Four structural mutations were detected by visual analysis of the gels. Computer analysis of gels corresponding to the mutant clones was also undertaken. At a spot size threshold of 200 spots to be matched using a computer algorithm, all four mutant polypeptides were detected. These results indicate the usefulness of the two-dimensional approach for mutagenesis studies at the protein level.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 20-33 
    ISSN: 0887-3585
    Keywords: calmodulin ; peptide ; calmodulin-binding peptide ; peptide design ; hydrophobic moment ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A basic, amphiphilic α helix is a structural feature common to a variety of inhibitors of calmodulin and to the calmodulin-binding domains of myosin light chain kinases. To aid in recognizing this structural feature in sequences of peptides and proteins we have developed a computer algorithm which searches for sequences of appropriate length, hydrophobicity, helical hydrophobic moment, and charge to be considered as potential calmodulin-binding sequences. Such sequences occurred infrequently in proteins of known crystal structure. This algorithm was used to find the most likely site in the catalytic (γ) subunit of phosphorylase b kinase for interaction with calmodulin (the δ subunit). A peptide corresponding to this site (residues 341-361 of the γ subunit) was synthesized and found to bind calmodulin with approximately an 11 nM dissociation constant. A variant of this peptide in which an aspartic acid at position 7 in its sequence (347 of the γ subunit) was replaced with an asparagin was found to bind calmodulin with approximately a 3 nM dissociation constant.
    Additional Material: 8 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 34-41 
    ISSN: 0887-3585
    Keywords: adrenergic receptors ; affinity chromatography ; electron microscopy ; oligomeric structure ; target size analysis ; HPLC digest mapping ; receptor evolution ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: We have characterized the structure of purified beta-adrenergic receptors by a combination of photoaffinity labeling, high performance liquid chromatography (HPLC)-tryptic mapping, CNBr fragmentation, target size analysis, and electron microscopy of purified receptor molecules. Guinea pig lung beta-adrenergic receptors purified by affinity chromatography, ion exchange chromatography, and HPLC size exclusion chromatography or photoaffinity labeled with [125]-iodocyanopindolol diazirine displayed mobilities on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) that corresponded to Mr = 68,000. Purified, radioiodinated guinea pig lung beta-receptors were subjected to complete trypsin digestion and subsequent reverse-phase HPLC analysis, which revealed nine peptides. Active site labeling and tryptic digestion of partially purified hamster lung beta-receptors produced one peptide, whereas CNBr digestion of the same material produced two labeled fragments, yielding information about the location of the active site within the primary sequence. Purified guinea pig lung receptors were examined with transmission electron microscopy. Electron micrographs revealed slightly asymmetric, rod-shaped structures with an average length of 13 nm and width of 3.4 nm. Many receptors were arranged as apparent dimeric structures. These findings confirm data obtained from target size analysis of guinea pig lung beta-receptors in situ which suggest that receptors may exist as oligomeric arrays in the native membrane. Taken together, these data provide information about putative functional domains of the beta-adrenergic receptor and its quaternary structure.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 54-63 
    ISSN: 0887-3585
    Keywords: domain association ; protein folding ; viscosity dependence ; solvent effects ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The equilibria and kinetics of ureainduced unfolding and refolding of the α subunit of tryptophan synthase of E. coli have been examined for their dependences on viscosity, pH, and temperature in order to investigate the properties of one of the rate-limiting steps, domain association. A viscosity enhancer, 0.58 M sucrose, was found to slow unfolding and accelerate refolding. This apparently anomolous results was shown to be due to the stabilizting effect of sucrose on the folding reaction. After accounting for this stabilization effect by using linear free-energy plots, the unfolding and refolding kinetics were found to have a viscosity dependence. A decrease in pH was found to stabilize the domain association reaction by increasing the refolding rate and decreasing the unfolding rate. This effect was accounted for by protonation of a single residue with a pK value of 8.8 in the native state and 7.1 in the intermediate, in which the two domains are not yet associated. The activation energy of unfolding is 4.8 kcal/mol, close to the diffusion limit. The negative activation entropy of unfolding, -47 cal/deg-mol, which controls this reaction, may result from ordering of solvent about the newly exposed domain interface of the transition state. These results may provide information on the types of noncovalent interactions involved in domain association and improve the ability to interpret the folding of mutants with single amino-acid substitutions at the interface.
    Additional Material: 8 Ill.
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  • 7
    ISSN: 0887-3585
    Keywords: proteolytic cleavage ; immunological cross-reaction ; amber fragment ; temperature-sensitive mutant ; stationary growth-phase ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Immunological cross-reaction was employed for identification of proteolytic fragments of E. coli RNA polymerase genered both in vitro and in vivo. Several species of partially denatured but assembled RNA polymerase were isolated, which were composed of fragments of the two large subunits, β and β′, and the two small and intact subunits, α and σ. Comparison of the rate and pathway of proteolytic cleavage in vitro of unassembled subunits, subassemblies, and intact enzymes indicated that the susceptibility of RNA polymerase subunits to proteolytic degradation was dependent on the assembly state.Using this method, degradation in vivo was found for some, but not all, of the amber fragments of β subunit in merodiploid cells carrying both wild-type and mutant rpoB genes. Although the RNA polymerase is a metabolically stable component in exponentially growing cells of E. coli, degradation of the full-sized subunits was found in two cases, i.e., several temperature-sensitive E. coli mutants with a defect in the assembly of RNA polymerase and the stationary-phase cells of a wild-type E. coli. The in vivo degradation of RNA polymerase was indicated to be initiated by alteration of the enzyme structure.
    Additional Material: 9 Ill.
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  • 8
    ISSN: 0887-3585
    Keywords: intrahelical ion pairs ; frequency of ion pairs in exposed helices ; alpha-helix stabilization ; protein tertiary structure stabilization ; protein-folding pathway ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A survey of 47 globular proteins was made to determine the probability of occurrence of ion pairs separated by 1, 2, 3, … and 8 residues in the alpha helices. As a control, the probability of occurrence of like charged pairs was also determined. The survey showed that ion pairs of the type i, i±3 and i, i±4 are the most predominant. Such a preference was not observed for like charged pairs. The observed frequency of ion pairs is significantly greater than their expected frequency. The normalized frequencies of occurrence of the ion pairs were also found to increase generally with the helix length. These results indicate that the ion pairs may contribute to the stability of solvent-exposed alpha helices. Since the stabilization of protein secondary structure, these results may throw light on the mechanism of protein folding.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 72-77 
    ISSN: 0887-3585
    Keywords: CO equilibrium constants ; des-(Arg 141α)HbA ; heme proteins ; high-affinity state ; kinetics ; ligand binding ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A few years ago we reported that histidine (HC3) 146β plays a major role in the pH-dependent propeties of the R-state of human hemoglobin, accounting for close to 50% of the R-state Bohr effect. We have extended these studies by examining the role of arginine 141α, another group known to affect the overall Bohr effect. We have compared the pH dependencies of the rate constants for the dissociation and combination of the fourth carbon monoxide molecule, I4 and I′4, respectively, for native hemoglobin A (HbA) and a control reconstututed HbA, and des-(Arg 141α) HbA, the hemoglobin molecule resulting from the enzymatic removal of the C-terminal arginine of the α-chain of human Hb. From these kinetic contants the pH dependence of L4, by about 80% between pH 6 and 8, where the aldkaline Bohr effect normally occurs, The sum of the effects of the removal of His 146β and of Arg 141α is grater than 100%. This suggests that at least one of these modifications altrs the contrubutions of other residues of this Bohr effect.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987) 
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
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  • 11
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 79-80 
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
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  • 12
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 90-110 
    ISSN: 0887-3585
    Keywords: compact units ; coefficient of compactness ; folding intermediates ; protein structural hierarchy ; primitive units ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The coefficient of compactness was recently introduced and used to locate domains in lysozyme and ribonuclease (Zehfus and Rose: Bio-chemistry 25:5759-5765, 1986). Nineteen additional proteins now have been analyzed by using this measure. Complete listings of compact units and plots showing their hierarchic organization are presented for all twenty-one proteins. Large compact units correspond well to protein domains; however, many smaller compact structures of equal or better compactness are also found. Since small compact units could represent subdomains or protein-folding intermediates, their structural composition is further examined.
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  • 13
    ISSN: 0887-3585
    Keywords: hybrid immunologlobulin ; compatible plasmids ; transfection ; mouse IgG1 ; mouse IgG2a ; dansyl ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: We have produced a series of hybrid IgG1-IgG2a mouse immunoglobulins with identical light chains (L) and variable regions to facilitate the identification of structural features associated with functional differnces between immunoglobulin isotypes. Hybrid heavy chain (H) constant region gene segments were generated by genetic recombination in Escherichia coli between plasmids carrying mouse γ1 and γ2a gene segments. Crossovers occured through out these segments although the frequency was highest in regions of high nucleotide sequence homology. Eleven variant immunoglobulins produced by transfected hybridoma cell lines are assembled into H2L2 tetramers and properly glycosylated. In addition, all 11 immunoglbulins have identical antigen combining sites specific for the fluorescent hapten ε-dansyll-L-lysine. Protein A binding was used as probe of the structural integrity of the Fc portion of the variant antibodies. Differeneces in protein A binding between IgG1 and IgG2a appear to be due to amino acid differances at postions 252 (Thr→Met) and 254 (Thr→Ser) of the heavy chain (EU numbering).
    Additional Material: 8 Ill.
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  • 14
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 111-117 
    ISSN: 0887-3585
    Keywords: crystallography ; antigen ; glycoprotein ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Neuraminidases from different subtypes of influenza virus are characterized by the absence of serlogical cross-reactivity and an amino acid sequence homology of approximately 50%. The three-dimensional structure of the neuraminidase antigen of subtype N9 from an avian influenza virus (A/tern/Australia/G70c/75) has been determined by X-ray crystallography and shown to be folded similarly to neuraminidase of subtype N2 isolated from a human influenza virus. This result demontrates that absence of immunological cross-reactivity is no measure of dissimilarity of polypeptide chain folding. Small differences in the way in which the subunits are organized around the molecular fourfold axis are observed. Insertions and deletions with respect to subtype N2 neuraminidase occur in four regions, only one of which is located within the major antigenic determinants around the enzyme active site.
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  • 15
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 118-129 
    ISSN: 0887-3585
    Keywords: homologous proteins ; hydropathy index ; chain flexibility ; α/β barrels ; tryptophan ; synthase aplha subunit ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The amino acid sequences of the α subunits of tryptophan synthase form ten different microorganisms were alingned by standard procedures. The α helics, β strands and turns of each sequence were predicted separately by two standard prediction algorithms and averaged at homologous sequence positions. Additional evidence for conserved secondary structure was derived form profiles of average hydropathy and chain flexibility values, leading to a joint prediction. There is good agreement between (1) predicted β strands, maximal hydropathy and minimal flexibility, and (2) predicted loops, great chain flexibility, and protein segments that accept insertions of various lengths in individual sequences. The α subunit is predicted to have eight repeated β-loop-α-loop motifs with an extra N-terminal α helix and an intercalated segment of highly conserved residues. This pattern suggests that the teritiary structure of the α subunit is an eightfold α/β barrel. The distribution of conserved amino acid residues and publilshed data on limited proteolysis, chemical modification, and mutagenesis are consistent with the α/β barrel structure. Both the active site of the α subunit and the combining site for the β2 subunit are at the end of the barrel formed by the carboxyl-termini of the β strands.
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  • 16
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 130-152 
    ISSN: 0887-3585
    Keywords: amino acid hydophobicity scale ; QSAR ; amino acids ; peptide side chains ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The fragment method of calculation partition coefficients (P) has been extended to include the common amino acids (AAs). The results indicate that polar and charged side chains influence the hydrophobicity of atoms in the side chain in a predictable manner. Feild effects, as evidenced through polar proximity factors and bond factors, need to be considered for accurate estimation of transfer phenomena. The calculated log P and ΔG°′ values of the 20 AAs agree well with the observed values. Pro calculates to be more hydrophilic than the observed log P. Hydrophobicity scales for peptide side chain residues are compared and evaluated in terms of suitability. Calculated π values for nonpolar side chain residures agree well with the observed values; calculated values for uncharged polar side chain residues deviate by about 0.6 log units except for Gln and Cys; and polar side chain residues with charged side chains calculate as too hydorphilic. Reasons for the differences are explored. We also suggest that tightly bound water to polar moieties in amino acids and peptides may be transferred into the octanol phase during partitioning experiments. A quantitative methodology is persented which characterizes the thermodynamic partitioning of groups and individual atoms in amino acids and proteins.
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  • 17
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987) 
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 18
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 162-166 
    ISSN: 0887-3585
    Keywords: protein folding ; secondary structure prediction ; tertiary structure prediction ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: In recent years, the protein-folding problem has attracted the attention of molecular biologists. Efforts have focused on developing heuristic and energy-based algorithms to predict the three-dimensional structure of a protein from its amino acid sequence. We have applied a series of heuristic algorithms to the sequence of human growth hormone. A family of five structures which are generically right-handed fourfold α-helical bundles are found from an investigaion of ∼108 structures. A plausible receptor binding site is suggested. Independent crystallographic analysis confirms some aspects of these predictions. These methods only deal with the “core” structure, and conformations of many residues are not defined. Further work is required to identify a unique set of coordinates and to clarify the topological alternatives available to α-helical proteins.
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  • 19
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 153-161 
    ISSN: 0887-3585
    Keywords: accessbility ; hydrophobic effect ; protein conformation ; Boltzmann statistics ; maximum likelihood ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Globular proteins fold into compact particles with interior amino acid residues shielded from the surounding aqueous environment. An early hypothesis holds that entropic hydophobic forces dirve this phenomenon. However, previous analyses based on a binary description of the accesible surfaces of amino acid residues in proteins did not support theis hypothesis. This report shows that a complete description of accessible surface areas is given by parametric distribution fuctions with three modes. The modes are formed by partitioning the available accessible surface area of the amino acids into three segments; the data for each segment are characterized by a mode-specific model. In the “repulsive” mode, probabilities of accessibility decrease exponentially with exposed surface area, as predicted by the hydrophobic hypothesis. A distinct “buried” mode is needed to account for an excess of residues at or near zero accessibility for most amino acids, consistent with the use of binary descriptions of accessibility. A third mode exists which is termed “near neutral” because it is described by a nearly uniform distribution of accessibility for the hydrophiliic amino acids. Empirical energies calculated for the repulsive mode correlate well with measured free energies of transfer of amino acids from water to organic solvents, while those from the buried mode correlate well with measured free energies of hydration of the side chains. Poor cross correlations between these energies give an explanation for the previous conflict in interpreting these data.
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  • 20
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 177-187 
    ISSN: 0887-3585
    Keywords: evolution ; protein structure ; nucleotide binding domain ; gene sequence ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The intron/exon organization of the human gene for glycogen phosphorylase has been determined. The segments of the polypeptide chain that corresponds to the 19 exons of the gene are examined for relationships between the three-dimensional structure to the protein and gene structure. Only weak correlations are observed between domains of phosphorylase and exons. The nucleotide binding domains that are found in phosphorylase and other glycolytic enzymes are examined for relationships between exons of the genes and structures of the domains. When mapped to the three-dimensional structures, the intron/exon boundaries are shown to be widely distributed in this family of protein domains.
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  • 21
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 167-176 
    ISSN: 0887-3585
    Keywords: icosahedral ; insect ; virus ; structure ; evolution ; nodavirus ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: We report the first atomic resolution structure of an insect virus determined by single crystal X-ray diffraction. Black beetle virus has a bipartite RNA genome encapsulated in a single particle. The capsid contains 180 protomers arranged on a T = 3 surface lattice. The quaternary organization of the protomers is similar to that observed in the T = 3 plant virus structures. The protomers consist of a basic, crystallographically disordered amino terminus (64 residues), a β-barrel as seen in other animal and plant virus subunits, an outer protrusion composed predominantly of β-sheet and formed by three large insertions between strands of the barrel, and a carboxy terminal domain composed of two distorted helices lying inside the shell. The outer surfaces of quasi-threefold related protomers form trigonal pyramidyl protrusions. A cleavage site, located 44 residues from the carboxy terminus, lies within the central cavity of the protein shell.The structural motif observed in BBV (a shell composed of 180 eight-stranded antiparallel β-barrels) is common to all nonstatellite spherical viruses whose structures have so far been solved. This highly conserved shell architecture suggests a common origin for the coat protein of spherical viruses, while the primitive genome structure of BBV suggests that this insect virus represents an early stage in the evolution of spherical viruses from cellular genes.
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  • 22
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 188-201 
    ISSN: 0887-3585
    Keywords: NMR ; NOE ; protein conformation ; structure data base ; structure fragments ; modelling ; distance matrices ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A method to build a three-dimensional protein model from nuclear magnetic resonance (NMR) data using fragments from a data base of crystallographically determined protein structures is presented. The interproton distances derived from the nuclear Overhauser effect (NOE) data are compared to the precalculated distances in the known protein structures. An efficient search algorithm is used, which arranges the distancs in matrices akin to a Cα diagonal distance plot, and compares the NOE distance matrices for short sequential zones of the protein to the data base matrices. After cluster analysis of the fragments found in this way, the structure is built by aligning fragments in overlapping zones. The sequentially long-range NOEs cannot be used in the initial fragments search but are vital to discriminate between several possible combinations of different groups of fragments. The method has been tested on one simulated NOE data set derived from a crystal structure and one experimental NMR data set. The method produces models that have good local structure, but may contain larger global errors. These models can be used as the starting point for further refinement, e.g., by restrained molecular dynamics or interactive graphics.
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  • 23
    ISSN: 0887-3585
    Keywords: myosin light chain kinase ; trace acetylation ; label selection ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A method is described for rapidly surveying the effects of modifying individual amino acid residues of a protein on its ability to interact specifically with another macromolecule. The procedure has been used to examine the individual roles of the seven lysyl residues of calmodulin in its ability to bind to smooth muscle myosin light chain kinase; previous studies by Jackson et al. (J. Biol. Chem. 261:1226-12232, 1986) have suggested that certain lysines may be located close to the interaction site. Trace [3H]-acetylated calmodulin, consisting predominantly of molecules acetylated at single sites together with unmodified protein, was incubated in excess (five- to 20-fold) with smooth muscle MLC kinase to allow the modified and unmodified molecules to compete for binding to the enzyme. Subsequently, the calmodulin-enzyme complex was separated from unbound calmodulin, and the level of acetylation of each of the seven lysines of the bound fraction of calmodulin was determined and compared to that of each corresponding group of the starting preparation. Significant changes were found at only two of the lysines, 21 and 75, where the extent of acetylation in the bound fraction was three- and fivefold lower, respectively, than that in the original preparation. These results were reproducible in three separate selection experiments employing both chicken and turkey gizzard MLC kinase. It is concluded that acetylation of calmodulin at either lysine 21 or 75 markedly reduces its affinity for MLC kinase, but acetylation at any of the other lysines (13, 30, 77, 94, or 148) has only minor effects. This finding supports the proposal that the face of the central helix containing lysine 75 is involved in interaction with MLC kinase and suggests also that additional contact near Ca2-binding site 1 occurs.
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  • 24
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    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 225-235 
    ISSN: 0887-3585
    Keywords: allosteric ; tissue-specific isozymes ; protein structure ; AMP ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Glycogen phosphorylases catalzye the regulated breakdown of glycogen to glucose-1-phosphate. In mammals, glycogen phosphorylase occurs in three different isozymes called liver, muscle and brain after the tissues in which they are prefer entially expressed. The muscle isozyme binds and is activated cooperatively by AMP. In contrast, the liver enzyme binds AMP noncooperatively and is poorly activated. The amino acid sequence of human liver phosphorylase is 80% identical with rabbit muscle phosphorylase, and those residues which contact AMP are conserved. Using computer graphics software, we replaced side chains of the known rabbit muscle structure with those of human liver phosphorylase and interpreted the effects of these changes in order to account for the biochemical differences between them. We have identified two substitutions in liver phosphorylase potentially important in altering the cooperative binding and activation of this isozyme by AMP.
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  • 25
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    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 260-261 
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
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  • 26
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    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 236-259 
    ISSN: 0887-3585
    Keywords: atomic probability distributions of proteins ; anisotropy and anharmonicity of motions in proteins ; multiple occupancy of atomic positions in proteins ; molecular dynamics simulation ; lysozyme ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Positional probability density functions (pdf) for the atomic fluctuations are determined from a molecular dynamics simulation for hen egg-white lysozyme. Most atoms are found to have motions that are highly anisotropic but only slightly anharmonic. The largest deviations from harmonic motion are in the direction of the largest rms fluctuations in the local principal axis frame. Backbone atoms tend to be more nearly harmonic than sidechain atoms. The atoms with the largest anharmonicities tend to have pdfs with multiple peaks, each of which is close to harmonic. Several model pdfs are evaluated on the basis of how well they fit probability densities from the dynamics simulations when parameterized in terms of the moments of the distribution. Gram-Charlier and Edgeworth perturbation expansions, which have been successful in describing the motions of small molecules in crystals, are shown to be inadequate for the distributions found in the dynamics of proteins. Multipeaked distribution functions are found to be more appropriate.
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  • 27
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    Proteins: Structure, Function, and Genetics 2 (1987), S. 210-224 
    ISSN: 0887-3585
    Keywords: protein folding ; circular dichroism ; protein secondary structure ; heuristic prediction of protein structure ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The tertiary structure of the α-subunit of tryptophan synthase was proposed using a combination of experimental data and computational methods. The vacuum-ultraviolet circular dichroism spectrum was used to assign the protein to the α/β-class of supersecondary structures. The two-domain structure of the α-subunit (Miles et al.: Biochemistry 21:2586, 1982; Beasty and Matthews: Biochemistry 24:3547, 1985) eliminated consideration of a barrel structure and focused attention on a β-sheet structure. An algorithm (Cohen et al.: Biochemistry 22:4894, 1983) was used to generate a secondary structure prediction that was consistent with the sequence data of the α-subunit from five species. Three potential secondary structures were then packed into tertiary structures using other algorithms. The assumption of nearest neighbors from second-site revertant data eliminated 97% of the possible tertiary structures; consideration of conserved hydrophobic packing regions on the β-sheet eliminated all but one structure. The native structure is predicted to have a parallel β-sheet flanked on both sides by α-helices, and is consistent with the available data on chemical cross-linking, chemical modification, and limited proteolysis. In addition, an active site region containing appropriate residues could be identified as well as an interface for β2-subunit association. The ability of experimental data to facilitate the prediction of protein structure is discussed.
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  • 28
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    Proteins: Structure, Function, and Genetics 2 (1987) 
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
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  • 29
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    Proteins: Structure, Function, and Genetics 2 (1987), S. 263-272 
    ISSN: 0887-3585
    Keywords: picornavirus ; capsid structure ; homology ; sequence comparisons ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: An attempt has been made to build a model of human rhinovirus 2 (HRV2) based on the known human rhinovirus 14 (HRV14) structure. HRV2 was selected because its amino acid sequence is known and because it belongs to the minor rhinovirus receptor class as compared to HRV14, which belongs to the major class. Initial alignment of HRV2 with HRV14 based on the primary sequence and the knowlege of the three-dimensional structure of HRV14 showed that most probable position of the majority of insertions and deletions occurred in the vicinity of the neutralizing immunogenic sites (NIm). Out of a total of 855 amino acids present in one copy of each of the capsid proteins VP1 through VP4 of HRV14, 411 are different between the two viruses. There are also 6 amino acids residues inserted and 14 residues deleted in HRV2 relative to HRV14. Examination of amino acid interactions showed several cases of conservation of function, e.g., salt bridges or the filling of restricted space. The largest variation amongst the residues lining the canyon, the putative receptor binding site, was in the carboxy-terminal residues of VP1.
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  • 30
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    Proteins: Structure, Function, and Genetics 2 (1987), S. 273-282 
    ISSN: 0887-3585
    Keywords: protein-DNA interactions ; hydroxylamine mutagenesis ; dimerization ; protein structure-function ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: EcoRI endonuclease mutants were isolated in a methylase-deficient background following in vitro hydroxylamine mutagenesis of plasmid pKG2 (Kuhn et al.: Gene 44:253-263, 1986). Mutants which survived high-level endonuclease expression (IPTG induction) were termed null mutants. Sixtytwo of 121 null mutants tested by Western blot contained normal levels of endonuclease cross-reacting protein. The complete endonuclease gene was scquenced for 27 null mutants. This group was found to consist of 20 signle base-change missense mutations, 6 double mutations, and 1 triple mutation. Ten of the 20 signle mutations were clustered between residues 139 and 144. When examined with respect to the structure of the EcoRI-DNA complex (McClarin et al.: Science 234:1526-1541, 1986), these alterations werre found to fall predominantly into two classes: substitutions at the protein-DNA interface or substitutions at the protein-protein (dimer) interface. Protein from several of the mutants was purified and sized by using HPLC. Wild-type EcoRI endonuclease and protein from three of the DNA interface mutations (A1a139→Thr, Gly140→Ser, Arg203→Gln) appeared to be dimeric, while protein from subunit interface mutations (Glu144→Lys, Glu152→Lys, Gly210→Arg) migrated as monomers.
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  • 31
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    Proteins: Structure, Function, and Genetics 2 (1987), S. 283-289 
    ISSN: 0887-3585
    Keywords: bent DNA ; electrostatics ; base-pair rolls ; finite difference calculations ; gene activation ; DNA-protein complex ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Two observations suggest that DNA, upon binding to E. coli catabolite gene activator protein (CAP), is sharply bent by a total angle of at least 100-150 degrees: (1) The electrostatic protential field of CAP shows regions of positive potential that from a ramp on 3 sides of the protein. (2) The DNA binding site size as determined by DNA ethylation interference with binding, (Majors: “Control of the E. coli Lac Operon at the Molecular Level.” Ph.D. Thesis, Harvard University, Cambridge, 1977) and by relative affinities of DNA fragments of various lengths (Liu-Johnson et al.: Cell 47:995-1005, 1986) requires severe bending of the DNA to maintain its favorable electrostatic contact with the protein.
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  • 32
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    Proteins: Structure, Function, and Genetics 2 (1987), S. 290-297 
    ISSN: 0887-3585
    Keywords: mutants ; structural function relationships ; protein folding and stability ; catalysis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Uniquely among class A β-lactamases, the RTEM-1 and RTEM-2 enzymes contain a single disulfide bond between Cys 77 and Cys 123. To study the possible role of this naturally occurring disulfide in stabilizing RTEM-1 β-lactamase and its mutants at residue 71, this bond was removed by introducing a Cys 77 → Ser mutation. Both the wild-type enzyme and the single mutant Cys 77 → Ser confer the same high levels of resistance to ampicillin in vivo to Echerichia coli; at 30°C the specific activity of purified Cys 77 → Ser mutant is also the same as that of the wild-type enzyme. Also, neither wild-type enzyme nor the Cys 77 → Ser mutant is inactivated by brief exposure to p-hydroxymercuri-benzoate. However, above 40°C the mutant enzyme is less stable than wild-type enzyme. After introduction of the Cys 77 → Ser mutation, none of the double mutants (containing the second mutations at residue 71) confer resistance to ampicillin in vivo at 37°C; proteins with Ala, Val, Leu, Ile, Met, Pro, His, Cys, and Ser at residue 71 confer low levels of resistance to ampicillin in vivo at 30°C. The use of electrophoretic blots stained with antibodies against β-lactamase to analyze the relative quantities of mutant proteins in whole-cell extracts of E. coli suggests that all 19 of the doubly mutant enzymes are proteolyzed much more readily than their singly mutant analogues (at Thr 71) that contain a disulfide bond. Thus, the disulfide bond of the RTEM-1 β-lactamase seems able to reduce the destabilizing effect of mutations at Thr 71. These results also emphasize the unique and essential role that Thr 71 performs in the stable folding of RTEM-1 β-lactamase and presumably the other class A β-lactamases.
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  • 33
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    Proteins: Structure, Function, and Genetics 2 (1987), S. 330-339 
    ISSN: 0887-3585
    Keywords: van der Waals radii ; conformation ; amino acid residue ; dipeptide approximation ; molecular modeling ; systematic conformationl search ; N-alkyl amino acid ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Effective van der Waals radii were celebrated in such a way that molecular models built from standard bond lengths and bond angels reproduced the amino acid conformations observed by crystallography in proteins and peptides. The celebrations were based on the comparision of the Ramachandbran plots prepared from high-resolution X-ray data of protins and peptides with the allowed φ,ψ torsional angel space for the depeptide molecular models. The celebrated radii are useful as criteria with which to filter energetically improbable conformations in molecular modeling studies of proteins and peptides.
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  • 34
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    Proteins: Structure, Function, and Genetics 2 (1987), S. 308-329 
    ISSN: 0887-3585
    Keywords: conformational dynamics ; normal mode analysis ; Young's modulus ; rigid structural elements ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The normal mode analysis of conformational fluctuation is carried out for a small globular protein, bovine pancreatic trypsin inhabitor. Results are analyzed mainly to reveal the mechanical construction of the protein molecule. We take dihedral angles, including peptide ω angles, as independent variables for the normal mode analysis. There are 306 such angles in this molecule. Motions in modes with frequencies lower than 120 cm-1 are showned to involve atoms in the whole protein molecule, and spatial change of displacement vectors is continues, i.e., those of atoms near in space are similar. To quantitate the observation of the continuity, a correlation function of direction vectors of atomic displacement is calculated. From this function we define a Quantity that is interpreted as the wave length of an equivalent elastic plane wave. From this Quantity we deduce eefective young's modulus for each mode. For the mode with the lowest frequency 4.4 cm-1, it terned out to be 0.8 × 109 dyn cm-2, the value two orders magnitude softer than, for instance, α-helices. Prompted by this observation, the four lowest frequency modes and also the harmonic motions in the thermal equilibrium are analyzed further mainly to detect relatively rigid structural elements in the molecule. From this analysis emerges a mechanical picture of the protein molecule that is made up of relatively rigid elements held together by very soft parts.
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  • 35
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    Proteins: Structure, Function, and Genetics 2 (1987), S. 298-307 
    ISSN: 0887-3585
    Keywords: α-bungarotoxin ; neurotropism ; rhabdo-virus ; α-subunit ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Peptides corresponding to portions of loop 2 of snake venom curare-mimetic neurotoxins and to a structually similar region of rabies virus glycoprotein were synthesized. Interaction of these peptides with purified Torpedo electric organ acetylcholine receptor was tested by measuring their ability to block the binding of 125I-labeled α-bungarotoxin to the receptor. In addition, inhibition of α-bungarotoxin binding to a 32-residue synthetic peptide corresponding to positions 173-204 of the α-subunit was determined. Neurotoxin and glycoprotein peptides corresponding to toxin loop 2 inhibited labeled toxin binding to the receptor with IC50 values comparable to those of nicotine and the competitive antagonist d-tubocurarine and to the α-subunit peptides with apparent affinities between those of d-tubocurarine and α-cobratoxin. Substitution of neurotoxin residue Arg37, the proposed counterpart of the quatenary ammonium of acetylcholine, with a negatively charged Glu residue reduced the apparent affinity about 10-fold. Peptides containg the neutotoxin invarint residue Trp29 had 10- to 100-fold higher affinites than peptides lacking this residue. These results demonstrate that relatively short synthetic peptides retain some of binding ability of the native protein from which they are derived, indicating that such peptides are useful in the study of proetin interactions. The ability of the peptides to compete α-bungarotoxin binding to the receptor with apparent affinites comparable to those of other cholinergic ligands indicates that loop 2 of the neurotoxins and the strucually similar segment of the rabies virus glycoprotein act as recognition sites for the acetylcholine receptor. Invarient toxin residues Arg37 and Trp29 and their viral homologs play important, although not essential, roles in binding, possibly by interaction with complementary anionic and hydrophobic subsites on the acetylcholine receptor. The α-subunit peptide most likely contains all of the determinants for binding of the toxin and glycoprotein peptides present on the α-subunit, because these peptides bind to the 32-residue α-subunit peptides with the same or greater affinity as to the intact subunit.
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  • 36
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    Proteins: Structure, Function, and Genetics 2 (1987), S. 340-358 
    ISSN: 0887-3585
    Keywords: artificial intelligence ; expert systems ; constraint satisfaction ; protein solution structure ; PROTEAN ; Nuclear Overhauser Effect ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A new method for the analysis of NMR data in terms of the solution structure of proteins has been developed. The method consists of two steps: first systematic search of the conformational space to define the region allowed by the initial set of experimental constraints, and second, the narrowing of this region by the introduction of aaditional constraint and optional refinement procedures. The search of the conformational space is guided by heuristics to make it computationally feasible. The method is therfore called the heuristic refinement method and is coded in an expert system called PROTEAN. The paper describe the validation of the first step of the method using an artificial NMR data set generated from the known crystal structure of sperm whale carbon monoxymyoglodin. It is shown that the initial search procedure yields a low-resolution structure of the myoglobin molecule, accurately reproducing its main topological features, and that the precision of the structure depend on the quality of the intial data set.
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  • 37
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    Biotechnology and Bioengineering 29 (1987), S. 8-15 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The production of Leuconostoc mesenteroides sucrose phosphorylase has been studied in 10- and 20-L batch fermentations. A fermentation medium was devised combining rapid growth, high cell yield, and high enzyme levels. Overall fermentation dynamics and enzyme fermentation patterns are elucidated here in detail. Sucrose is phosphorolyzed into fructose and glucose-1-phosphate (G-1-P) with G-1-P preferentially utilized (thus saving ATP). Subsequently, fructose is gradually metabolized and is also converted to mannitol. Invertase activity is absent. Sucrose phosphorylase is formed transitorily with peak levels toward the end of active growth; a sharp decline in enzyme activity occurs upon further fermentation. The moment of cell (enzyme) harvest is thus critical in view of obtaining active cell or enzyme preparations for sucrose phosphorolysis. Microaerophilic and strictly anaerobic fermentations displayed no appreciable difference in sucrose phosphorylase formation profile. The enzyme is intracellularly located. It is constitutively formed in the absence of sucrose, contrary to that of Pseudomonas species; other disaccharide phosphorylases are not formed.
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  • 38
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    Biotechnology and Bioengineering 29 (1987), S. 793-795 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
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  • 39
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    Biotechnology and Bioengineering 29 (1987), S. 789-792 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Reliable dynamic descriptions of cellular growth are important for many practical applications including bioreactor design and control. A chemically structured growth model of Escherichia coli has been formulated and herein we focus on finding the essential dynamic order of the metabolic part of this model. Standard linear analysis is applied and the main finding is that the model contains three essential modes of motion over the time scale of growth. The doubling time is successfully predicted from an unstable growth motion and the metabolite composition of the three modes of motion suggests that only a three pool metabolic model is necessary. The three pools correspond to important groups of macromolecules; protein, nucleic acids and cell wall constituents.
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  • 40
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    Biotechnology and Bioengineering 29 (1987) 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
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  • 41
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    Biotechnology and Bioengineering 29 (1987), S. 796-798 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
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  • 42
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A respiratory-deficient, mutant of Kluyveromyces fragilis was isolated using a ethidium bromide mutagenesis. It was characterized by a loss of cytochromes a + a3 and by an improvement of its inulinase activity. Under anaerobic conditions this mutant was always better than the wild strain for ethanol production especially from Jerusalem artichoke extracts containing large amounts of high polyfructosans ("early" extracts).
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  • 43
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Continuous culture was employed to study plasmid instability in an amylase-producing Bacillus subtilis 1A289 that was genetically manipulated. No true steady state could be obtained with 1A289(pEAA)-strain (plasmid)-due to its structural instability, which occurred both with glucose and Maltrin-100 as limiting carbon sources. The plasmid, pEAA (CmR, amy+, i.e., chloramphenicol resistant, amylase positive) degenerated into a smaller plasmid, pEAA1 (CMR, amy-) that was stable. There was a direct correlation between amylase-producing ability and this structural instability since famy (fraction of cells with amylase-producing ability) reached zero at the same time that f (fraction of cells that are resistant to chloramphenicol) reached its maximum level. Since the deletion in pEAA was larger than the original amylase-gene insert, either all of part of the insert is absent from pEAA1. Though on discernible change in 1A289(pHV33), where pHV33 is the vector plasmid, was observed during continuous cultivation, its behavior was different from that of the stable 1A289(pEAA1).
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  • 44
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    Biotechnology and Bioengineering 29 (1987), S. 873-883 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Toluene was oxidized by a mutant strain of Pseudomonas putida (strain NG1) to toluene Cis-Glycol (TCG). Product was accumulated in fed-batch cultures to concentrations (18-24 g/L) higher than hitherto achieved. In vitro activities of toluene dioxygenase from P. Putida NG1 were fivefold lower than that from the toluene-grown wild-type organism, whereas comparable activities of both catechol 2,3- and catechol 1,2-oxygenase were obtained; irreversible inhibition of toluene dioxygenase activity by TCG was shown in vitro. Ammonia deprivation during the production phase limited the growth of revertant organisms but had little effect on either the duration (25h) of the process or the final concentration of TCG achieved. The rate of glucose utilization decreased throughout the biotransformation and cell death accompanied the cessation of TCG accumulation in cultures. These changes were a consequence of TCG formation and a cooperative toxic effect was demonstrated for toluene and TCG. Adenylate energy charge values decreased from ca. 0.8 to 0.2 over the course of the biotransformation but were maintained above 0.5 in the absence of TCG. Similarly, cellular AMP levels increased dramatically during biotransformation, presumably as a consequence of RNA degradation, but were maintained at low levels in the absence of TCG. The results suggest that TCG is the mediate of a gradual deterioration in the state of the culture which leads to a loss of both in vivo and in vitro toluence dioxygenase activity and a marked decrease in culture viability.
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  • 45
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    Biotechnology and Bioengineering 29 (1987), S. 482-487 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: L-Phenylalanine was produced continuously from L-as-partate and phenylpyruvate by transaminase from a newly screened Pseudomonas putida strain. The process was carried out with an isolated enzyme in homogeneous phase in an enzyme membrane reactor and with immobilized whole cells in a stirred tank reactor, respectively. Due to the difference in transport resistance, the productivity of the free enzyme in homogeneous phase (72 mmol/L h) was about 3 times higher than the productivity achieved using immobilized cells. However, a better stability of the biocatalyst was observed with immobilized cells.
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  • 46
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    Biotechnology and Bioengineering 29 (1987), S. 488-492 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: We describe a first-principles analysis of a system for the continuous culture of the green alga Scenedesmus obliquus under light-limiting conditions. According to this analysis, the productivity of the algal culture is given by the relation Y = EmI0AK(1 - e-αcl) - GRcV, where Y = yield (g cells/h), Em = 0.20 (the maximum attainable photosynthetic conversion on an energy basis), A = illuminated area (m2), K = 0.156[(g cells/h/W), the energy equivalent of the algae], I0 = light intensity (W/m2), α = extinction coefficient (L/cm/g),c = cell concentration (g/L), I = light path (cm), R = respiration rate (g carbon/g cells/h), V = culture volume (L), and G = ratio of g cells to g carbon (2.04). This formula is completely determined and has no free adjustable parameters. Using parameter values determined independently, the model accurately predicted the relationship of productivity to cell density in the culture system.
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  • 47
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    Biotechnology and Bioengineering 29 (1987), S. 493-501 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Biological denitrification of drinking water was studied in a fluidized sand bed reactor using a mixed culture. Hydrogen gas was used as the reaction partner. The reaction kinetics were calculated with a double Monod saturation function. The Ks value for hydrogen was below 0.1% of saturation. No appreciable biofilm diffusion effects were detected. Reactor performance was a function of the culture's past history. Batch experiments always exhibited an accumulation of NO2-, but continuous experiments with a sufficiently long residence time always resulted in complete nitrogen removal. Rates of up to 23 mg N/L h, 25 mg N/g DW h, and 7.9 mg H2/L h were achieved. Residence times of 4.5 h would be required for complete denitrification of water containing 25 mg NO3--N/L or approximately 1 h for every 5 mg/L.
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  • 48
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    Biotechnology and Bioengineering 29 (1987), S. 502-512 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The fermentation kinetics Zymomonas mobilis were studied near zero growth rate in fed-batch cultures and continuous cultures with complete cell recycle. The results show the ethanol enhances that specific substrate conversion rate under these conditions. The maximum achievable ethanol concentration in continuous cultures with cell recycle (66 g/L) was significantly lower than in fed-batch cultures (100 g/L). The results indicate that growth-rate-independent metabolism is not instantaneous and can lag behind steadily increasing ethanol concentrations in fed-batch fermentations. A model is proposed to account for this slow adaptation.
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  • 49
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    Biotechnology and Bioengineering 29 (1987), S. 520-528 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An on-line computer was used to control the ratio of carbon to nitrogen in algal biomass. An indirect method of growth and biomass estimation was utilized. This was based on balancing the amount of CO2 carbon in and out of the algal bioreactor. It was shown that growth conditions govern the morphology and composition of Spirulina platensis. Cells grown under light limitation were narrower, had high levels of phycocyanin pigments, and were packed full of small lipid granules. Whereas cells grown under nitrogen limitation lost their characteristic blue-green color, had reduced levels of phycocyanin, were fatter, and were packed full of larger lipid granules.
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  • 50
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    Biotechnology and Bioengineering 29 (1987), S. 165-170 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Pretreatment of lignocellulosic materials such as newspaper, rice straw, pulp waste, and municipal solid waste with hydrogen peroxide in the presence of manganese compounds greatly enhances their susceptibility to enzymatic saccharification. This pretreatment can be achieved using rather mild conditions with only a minimal decrease in the recovery and little change in composition. Manganese salts in this hydrogen peroxide pretreatment works effectively in particular when the concentration of hydrogen peroxide is relatively low. The susceptibility of hydrogen-peroxide-pretreated substrate to enzymatic saccharification increases with increasing the molar ratio of manganes to hydrogen peroxide up to 1 : 100.
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  • 51
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    Biotechnology and Bioengineering 29 (1987), S. 151-159 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Biodehalogenation of 10-5 M concentrations of bromotrichloromethane (BTM) and 1,2-dibromo-3-chloropropane (DBCP) was studied in static cultures of Pseudomonas putida PpG-786. The experimental cultures were prepared by growing P. putida on camphor, which is known to induce the synthesis of high concentrations of cytochrome P-450 in this bacterium. Measurements of bromide ion release were found to be approximately consistent with the amounts of halocarbon degraded. Gas chromatography/elctron capture detection (GC/ECD) measurements of hydrocarbon degradation products as a function of incubation time showed the transitory appearance of chloroform and bromodichloromethane from BTM and the transitory appearance of lower boiling but unidentified products from DBCP. The degradation of BTM to trihalomethanes and the halide ion is consistent with the enzymatic reductive dehalogenation by cytochrome P-450 reported by others. The dependence of initial conversion rates on halocarbon concentration (0.1-2 ppm) and cell mass concentration (1-28 g cell/L) was determined by measuring the decline of parent halocarbon in stirred batch cell suspensions. The rate of DBCP conversion was up to 10-fold higher than the rate of BTM conversion. When the intracellular, enzyme-catalyzed conversion BTM is analyzed by the effectiveness factor of heterogeneous catalysis, the initial conversion rates measured suggest that intrinsic enzyme kinetics, rather than halocarbon permeation of the cell membrane or other diffusive processes, is rate limiting.
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  • 52
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    Biotechnology and Bioengineering 29 (1987), S. 171-175 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Higher activity of ethanol production due to higher density of yeast cells was observed in yeast cells immobilized with artificial polymer carriers of higher water content based on methoxypolyethyleneglycol methacrylate and 2-hydroxyethylacrylate. These polymer carriers were prepared by radiation-induced polymerization below 0°C. Yeast cells were immobilized with these carriers by adsorption method during multiplication. Two possible reasons for higher activity were discussed.
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  • 53
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    Biotechnology and Bioengineering 29 (1987), S. 176-179 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Eight chemically modified cellulose supports were tested for their ability to absorb components of the Aspergillus niger cellulase system. At least two of the most effective adsorbents, aminoethyl cellulose and carboxymethyl cellulose, were shown to be useful for the fractionation of cellulases. These supports apparently owe their resolving capacity to both ion exchange and biospecific binding effects; however, the relative importance of each effect is unknown. These observations form the basis for a new cellulase fractionation technique, combined ion exchange-affinity chromatography.
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  • 54
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    Biotechnology and Bioengineering 29 (1987), S. 187-194 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Let us consider the modeling of a cascade reactor for the production of ethanol. The rates of reaction in alcoholic fermentation are modeled so that it can assume both ethanol and substrate inhibition, in relation to the observed results.A nonstructured model, based on biomass, substrate, and ethanol concentrations, is developed and identified. It is a complex model, this being due to the nonlinearity between the specific rate of ethanol production and the growth rate and, on the other hand, the study of the static optimization of ethanol fermentation is performed.
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  • 55
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    Biotechnology and Bioengineering 29 (1987), S. 180-186 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: There are many scaling formulas that predict the oxygen mass transfer coefficient as kL·a = constant·(Hp/V)αVsβ Exponents α and β frequently are scale dependent themselves. A general formula has been derived from the work of Calderbank,1 Miller,2 and Tilton,3 resulting in kL·a = C1 φ + C2 log (Pm/V) φ where φ equals the gas-holdup fraction and Pm/V equals the effective mechanical power input per unit of volume. This formula is consistent with the formula of Westerterp4 modified by Miller.2 Gas holdup can be predicted in several ways. Gas-sparged isothermal expansion power input, used for predicting φ, demonstrates that scaling can be done by using either superficial air velocity or volume per volume per minute for aeration.The importance of mixing in replenishing oxygen at the boundary layers of microorganisms will be assessed and compared with the kL·a as the oxygen transfer ratelimiting step.
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  • 56
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    Biotechnology and Bioengineering 29 (1987), S. 195-203 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In Part I1 of this research a complex model was obtained for describing the ethanol fermentation in a cascade reactor. This complexity is due to both the nonlinearity and the large scale representation. Based on techniques of partitioning and relaxation, a decentralized successive approximation method is developed for static optimization. The influence of the way of fermentation during continuous culture in multistage fermentors is studied in the case of a double inhibition of cell growth and product formation by both substrate and final product. The optimal number of reactors is discussed with respect to the strength of the ethanol inhibition, while the interest of head feeding or distributed feeding is evaluated in relation to the strength of substrate inhibition.
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  • 57
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    Biotechnology and Bioengineering 29 (1987), S. 204-214 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The electrochemical transient of a two-substrate enzyme electrode was studied theoretically and experimentally. Operation of such electrodes in the chronocoulometric mode leads to increased electrode sensitivity and makes possible the retrieval of useful information on transport and kinetics parameters. Digital simulation was used to solve the kinetics and transport equations and to produce the theoretical chronocoulometric response. A glucose electrode based on glucose oxidase crosslinked to different matrices was tested with air oxygen and p-benzoquinone as the cosubstrate. A computerized electrochemical system was employed for electrode potential control and data acquistion and analysis.
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  • 58
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    Biotechnology and Bioengineering 29 (1987), S. 215-221 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An auxotrophic mutant of Saccharomyces cerevisiae, containing a recombinant 2-μ-based plasmid, was grown in selective media in continuous culture. The plasmid retained the ability to synthesize acid phosphatase as product, which was deleted from the host. Plasmid loss was followed at various dilution rates, and the level of plasmid expression was controlled by changing the β-glycero/inorganic phosphate ratio.Some interesting trends were observed. As the level of plasmid expression was raised, the stability dropped markedly. Since acid phosphatase expression is regulated at the level of transcription, it is possible that increased transcription interfered with plasmid replication, hindered segregation, or overburdened the cell's DNA repair capability. It was also observed that plasmid stability was substantially increased at high growth rates. At dilution rates of 0.3 and 0.37 h-1, feeding only inorganic phosphate, the plasmid was completely stable.
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  • 59
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    Biotechnology and Bioengineering 29 (1987), S. 222-227 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A vortex chamber for continuous adsorption of the antibiotic Myxovirescin A on XAD resins was developed. In this paper the design and use of the vortex chamber in an external bypass of a continuous process is described. Compared with the normal continuous process, the specific production rate of the antibiotic is four to five times higher when the antibiotic is continuously adsorbed. A semicontinuous process could be performed by using two chambers for adsorption and regeneration alternatively.
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  • 60
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    Biotechnology and Bioengineering 29 (1987), S. 242-248 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The inhibitory effect of butanol on yeast growth has been studied for the strain Candida utilis ATCC 8205 growing aerobically on butanol under batch conditions. A mathematical expression was then proposed to fit the kinetic pattern of butanol inhibition on the specific growth rate: \documentclass{article}\pagestyle{empty}\begin{document}$$ \mu = \frac{{\mu _m S}}{{K_s + S}}\left[{1 - \frac{S}{{S_m }}} \right]^n $$\end{document}The maximum allowable butanol concentration above which cells do not grow was predicted to be 9.16g/L. The proposed model appears to accurately represent the experimental data obtained in this study and the literature data developed for a variety of batch culture systems at widely ranging substrate concentrations.
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  • 61
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    Biotechnology and Bioengineering 29 (1987), S. 228-235 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Pretreatment methods were compared with steam explosion, and differing views on the relative importance of mechanical and chemical effects were outlined. Hydrolysis was desirable; pyrolysis was undesirable. The effects of initial moisture content on steam consumption, mechanism and rate of heat transfer, pentosan solubilization, and subsequent glucose yield were summarized. The insignificant effect, after treatment at 240°C, of 90% pressure bleed-down before explosion on subsequent simultaneous saccharification and fermentation (SSF) yields was described. Treatment at 190°C with complete bleed-down (no explosion), when compared with that at 240°C with explosion from full pressure, showed at least as good solubilizatoin of pentosan, enzymatic hydrolysis, and SSF but showed greater pentosan destruction for the same degree of pentosan removal. Water washing of unexploded steamed aspenwood chips was at least as efficient as that of similarly treated but exploded chips. Scanning electron micrographs of unexploded chips showed extensive rupturing of vessel pit membranes and other morphological features associated with steam-exploded wood. Neither the explosion nor the high temperatures (above 190°C) are necessary.
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  • 62
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    Biotechnology and Bioengineering 29 (1987), S. 625-632 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This study deals with the behavior of a heterogeneous multisubstrate enzymatic system under enzyme inactivation in a reaction. Electronic computer modeling data have been obtained for its macrokinetics at different modes: (1) under mixed inflow of the substrates and (2) under their spatial separation. The enzymatic membrane exhibits low sensitivity to a change in the external conditions as the substrates are intermixed on the boundary. Quite the contrary, in the case of spatial separation of the substrates, the product flow from the membrane has displayed abrupt fluctuations at different boundary conditions. This work also looks into the arrangement of the reaction zones in the membrane and their transitions under different conditions.
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  • 63
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    Biotechnology and Bioengineering 29 (1987), S. 236-241 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Commercial cellulase preparations from Trichoderma viride and Aspergillus niger were immobilized on porous silica glass and ceramics such as alumina and titania with titanium tetrachloride (TiCl4) and on their silanized derivatives with glutaraldehyde (GLUT). The amounts of the immobilized enzymes were in the range 10-50 mg/g carrier (dry) depending on the kind of carrier and immobilization method. Their activities toward carboxymethyl cellulose (CMC), xylan, aryl-β-glucoside, and aryl-β-xyloside were 3-53% of those of the native enzymes. The optimum pH of the enzymes shifted to the acidic side in most cases, whereas the optimum temperatures were nearly the same as those of native ones. The activity of immobilized enzyme preparations towards CMC did not change significantly during continuous operation over a periods of 60 days. Finally, xylan was hydrolyzed with the immobilized enzymes, and the sugars formed were investigated.
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  • 64
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    Biotechnology and Bioengineering 29 (1987), S. 1024-1034 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Techniques are reviewed for the identification and enrichment of fimbriae-positive and fimbriae-negative Escherichia coli. Fimbriae-positive E. coli were observed to form a semistable suspension of pH 7.0 which settled at a rate much slower than the fimbriae-negative bacteria. Intense autoflocculation of fimbriae-positive E. coli was noted at pH values below 5.2.
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  • 65
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    Biotechnology and Bioengineering 29 (1987) 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
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  • 66
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    Biotechnology and Bioengineering 29 (1987), S. 1040-1043 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
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  • 67
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    Biotechnology and Bioengineering 29 (1987), S. 1035-1039 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 4 Ill.
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  • 68
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    Biotechnology and Bioengineering 29 (1987), S. 1045-1049 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Batch ethanol fermentation by cells of Zymomomas mobilis ATCC 29191, ionically adsorbed on a DEAE-cellulose ion exchanger, was investigated in a stirred fermentor. Adsorption isotherms in different media were determined and used to interpret the effects of the environment on cell immobilization. Other factors affecting cell immobilization during an actual fermentation were studied. Mechanical agitation was found to cause detachment of cells from the ion exchange particles. The results suggest that the amount of cells adsorbed during a fermentation process is different from that found from adsorption isotherm data. Consequently, application of equilibrium adsorption data to actual fermentations should be done with caution.
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  • 69
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    Biotechnology and Bioengineering 29 (1987), S. 279-288 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Diffusion of gases through legume nodules is important for nitrogen fixation. A mathematical model is presented for diffusion and enzymatic reaction for legume nodules with a reactive core and an inert shell. The transient model is solved numerically for spherical geometry for acetylene reduction by nitrogenase enzyme. The results are used to estimate the diffusivities of acetylene and ethylene in the nodules by comparing predicted and experimental lag times. The experimental results are also analyzed using an effectiveness factor plot for spherical nodules with inert shells and reactive cores. The results show that the diffusivities are slightly higher than those for acetylene and ethylene in water because of some contribution of gas phase diffusion. Applications to oxygen diffusion through nodule tissue are suggested.
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  • 70
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    Biotechnology and Bioengineering 29 (1987), S. 705-713 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Homogeneous membranes containing immobilized glucose oxidase and catalase were stored in buffered solutions at 37°C to determine the mechanisms and rates of catalyst inactivation. The experiments were designed so that inactivation occurred homogeneously throughout the membrane, thereby simplifying the analysis. The mechanism of inactivation is consistent with the reaction of hydrogen peroxide and certain catalytic intermediates of both enzymes. Based on this information, numerical simulations were developed that incorporate spatially heterogeneous catalytic and inactivation processes.
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  • 71
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    Biotechnology and Bioengineering 29 (1987), S. 1066-1074 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The relationship between pressure and temperature as it affects microbial growth and metabolism has been examined only for a limited number of bacterial species. Because many newly-discovered, extremely thermophilic bacteria have been isolated from pressurized environments, this relationship merits closer scrutiny. In this study, the extremely thermophilic bacterium, Sulfolobus acidocaldarius, was cultured successfully in a hyperbaric chamber containing helium and air enriched with 5% carbon dioxide. Over a pressure range of approximately 1-120 bar and a temperature range of 67-80°C, growth was achieved in a heterotrophic medium with the air mixture at partial pressures up to 3.5 bar. Helium was used to obtain the final, desired incubation pressure. No significant growth was noted above 80°C over the same range of hyperbaric pressures, or at 70°C when pressure was applied hydrostatically. Growth experiments conducted under hyperbaric conditions may provide a means to study these bacteria under simulated in situ conditions and simultaneously avoid the complications associated with hydrostatic experiments. Results indicate that hyperbaric helium bioreactors will be important in the study of extremely thermophilic bacteria that are isolated from pressurized environments.
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  • 72
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    Biotechnology and Bioengineering 29 (1987), S. 714-728 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: There is good evidence that the specific feeding and growth rates of a population of suspension-feeding ciliates on a population of bacteria is described by the classic Monod model or something very like it. However, use of this model combined with the assumption that feeding of the ciliates is the only interaction between the populations leads to predictions grossly at variance with experimental observations. A second interaction between the populations, growth of the bacteria on products of lysis, and perhaps metabolism of the ciliates is known to occur and might be an important factor in determining the dynamics of ciliate-bacterial systems. Whether or not this is the case is examined in the present article. It is concluded that accounting for the second interaction does not remove the discrepancies between model predictions and experimental observations. It is concluded also that the second interaction is likely not important except in batchtype situations where the supply of available energy for supporting biological activity is not replenished.
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  • 73
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    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Alcohol fermentation of corn starch without cooking was performed by using Chalara paradoxa glucoamylase preparation, which had stronger raw starch digesting activity than those of the conventionally known glucoamylases. A raw corn starch-enzyme-yeast mixture was fermented optimally at pH 5.0 and 30°C for five days and produced ethanol. The yields of ethanol were between 63.5 and 86.8% of the theoretical value by baker's yeast (Saccharomyces cerevisiae), and between 81.1 and 92.1% of the theoretical value by sake yeast (Saccharomyces sake).
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  • 74
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    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A mechanistically detailed single-cell model E. coli B/r-A was adapted to simulate the effects of vector presence on cell metabolism. Competition for RNA polymerase between chromosome and plasmid DNA is explicitly included. Distribution of active ribosomes among chromosome- and plasmid-derived messenger RNA, another key facet of host-plasmid interactions, is also treated in detail. Simulations of recombinant cell growth rate and cloned-gene productivity as a function of relative plasmid number per cell agree closely with experimental results. Model prediction of the variation of cell cycle parameters C and D with plasmid number are roughly consistent with available data. Models of this class can be used to simulate changes in productivity resulting from specific alterations in the expression vector. The effects of changing cloned-gene promoter and ribosome binding strengths and of augmenting cell transcription or translation capacity have been studied using the recombinant cell model. Results suggest that cloned-gene expression is limited by cellular transcription capacity. These and other parametric studies, conveniently implemented using the computer cell, provide important guidance for future experiments directed at better understanding of host-plasmid interactions and at optimizing recombinant system productivity.
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  • 75
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    Biotechnology and Bioengineering 29 (1987), S. 329-334 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A study was performed to optimize the production of solvents from whey permeate in batch fermentation using Clostridium acetobutylicum P262. Fermentations performed at relatively low pH values resulted in high solvent yields and productivities, but lactose utilization was incomplete. At higher pH values, lactose utilization was improved but acid production dominated over solvent production. When operating at the higher pH values, an increase in the initial lactose concentration of the whey permeate resulted in lower rates of lactose utilization, and this was accompanied by increased solvent production and decreased acid production. Analysis of data from several experiments revealed a strong inverse relationship between solvent yield and lactose utilization rate. Thus, conditions which minimize the lactose utilization rate, such as low culture pH values or high initial lactose concentrations, favor solventogenesis at the expense of acid production.
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  • 76
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    Biotechnology and Bioengineering 29 (1987), S. 1105-1112 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Ethanol fermentation by yeast was carried out in a cell filtration recycle system with a hollow-fiber membrane filter. Maximum biomass concentrations up to 210 g dry wt/L were obtained, but in normal operation concentrations they were between 100 and 150 g/L. The ethanol productivity using 14% glucose feed was 85 g/L h, with an ethanol concentration of 65 g/L and an ethanol yield of over 90%. The ethanol productivity and yeast growth rate decreased as the cell concentration increased beyond a certain level. The cell mass in the reactor was maintained by a proper manipulation of diluticn rate and bleed ratio depending on the growth rate.
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  • 77
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    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Conditions for high-cell-density fermentations of Saccharomyces cerevisiae strains producing recombinant-DNA-derived proteins were established. Strains producing human immune interferon (IFN-γ) from the constitutive PGK promoter failed to grow to high cell densities and exhibited low plasmid stability. Regulated expression of IFN-γ was obtained in similar strains by employing a hybrid yeast GPD promoter that was subject to carbon source regulation due to the presence of regulatory DNA sequences from the yeast GAL 1,10 intergenic region. IFN-γ expression programmed by this vector was low during growth on glucose and was induced by galactose. Previously defined fermentation conditions employing glucose as a carbon source were applied to this strain, resulting in high ceil densities with higher plasmid stability. Various methods of galactose induction of IFN-γ expression in high-cell-density fermentations were investigated. Optimal conditions resulted in a 2000-fold induction and production of 2 g IFN-γ/L fermentation culture.
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    Biotechnology and Bioengineering 29 (1987), S. 1122-1126 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The experiment of bacteria adhesion onto starch granules is conducted. It is found that anaerobic saccharolytic bacteria have the highest adhesion ability in their growth and initial stage of stationary phase. Starch granules with a low crystallinity, low bulk density, and high water-holding capacity have a high adhesion capacity. The optimum temperature for both bacterial growth and their adhesion is 30°C. The optimum pH for the bacterial adhesion range from 5.0 to 6.5. Anaerobic conditions cause an appreciable decrease in percentage of adhesion. The percentage of adhesion is not sensitive to the type of soluble saccharide on which bacteria were grown.
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  • 79
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    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 29 (1987), S. 1127-1134 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Formula are developed for calculating the performance characteristics (surface-to-total-volume ratio, surface-to-packing-volume ratio, and void volume fraction) of four different types of immobilized cell modular units (ICMUs) for ethanol fermentation: plate-type, spiral-type, beehive-type and bead-type ICMUs. Examples are used to illustrate how the formulas are useful for investigating the effects of characteristic dimensions of packing geometry, as well as the effect of scale on the performance characteristics of the ICMUs.
    Additional Material: 8 Ill.
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  • 80
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A process for the microencapsulation of mammalian cells in a commercially available water-insoluble polyacrylate (EUDRAGIT RL) is described, and the effects of process parameters are outlined The polymer dissolved in diethyl phthalate was pumped along the annulus formed from two concentric needles, while the cell suspension was pumped inside the inner needle Droplets of polymer solution containing cells were blown off the end of the needles by a coaxial air stream. The droplets fell into a corn oil-mineral oil curing bath, in which the solvent was removed from the nascent capsule causing the polymer to precipitate around the cell suspension core. Capsules were washed free of oils and solvent in a fractionated plasma that allowed for quantitative transfer of capsules from the oil phase to an aqueous medium. By appropriate adjustment of the coaxial air flow rate, capsule size could be varied from 250-1000 μm, although the most convenient size was found to be 400-700 μm. Adding Ficoll 400 to the cell suspension to match the density of the suspension to the polymer solution resulted in capsules with a well-centered core but did not affect capsule strength. It appeared that increasing the polymer solution concentration or the polymer to the cell flow rate ratio resulted in an increased capsule strength, although differences in capsule size made unequivocal conclusions difficult. These capsules are of potential use as an artificial pancreas for the treatment of diabetes (with pancreatic islets) or for large-scale tissue culture and the production of bioactive products (e.g., with fibroblasts).
    Additional Material: 7 Ill.
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  • 81
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    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 29 (1987), S. 1151-1154 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The cellulase system of Bacteroides cellulosolvens was subjected to both catabolite repression and feedback inhibition by cellobiose. Cellulose-solubilizing activity was 50% inhibited at a cellobiose concentration of 2.6 g/L and completely inhibited by 12 g/L. Glucose at 12 g/L (the highest concentration tested) had no effect on cellulase activity. Supplementation of B. cellulosolvens cellulase with β-glucosidase resulted in increased conversion of cellobiose to glucose; however, a constant cellobiose pool size of approximately 7 g/L was maintained.
    Additional Material: 3 Ill.
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  • 82
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    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 29 (1987), S. 1144-1150 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Ethanolic fermentation of spent sulphite liquor with ordinary bakers' yeast is incomplete because this yeast cannot ferment the pentose sugars in the liquor. This results in poor alcohol yields, and a residual effluent problem By using the yeast Candida shehatae (R) for fermentation of the spent sulphite liquor from a large Canadian alcohol-producing sulphite pulp and paper mill, pentoses as well as hexoses were fermented nearly completely, alcohol yields were raised by 33%, and sugar removal increased by 46%. Inhibitors were removed prior to fermentation by steam stripping. Major benefits were obtained by careful recycling of this yeast, which was shown to be tolerant both of high sugar concentrations and high alcohol concentrations. When sugar concentrations over 250 g/L (glucose: xylose 70:30) were fermented, ethanol became an inhibitor when its concentration reached 90 g/L. However, when the ethanol was removed by low-temperature vacuum distillation, fermentation continued and resulted in a yield of 0.50 g ethanol/g sugar consumed. Further improvement was achieved by combining enzyme saccharification of sugar oligomers with fermentation. This yeast is able to ferment both hexoses and pentoses simultaneously, efficiently, and rapidly. Present indications are that it is well suited to industrial operations wherever hexoses and pentoses are both to be fermented to ethanol, for example, in wood hydrolysates.
    Additional Material: 7 Ill.
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  • 83
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    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 30 (1987), S. 306-313 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The effect of temperature and pH on the kinetics of ethanol production by free and calcium alginate immobilized cells of Kluyveromyces marxianus grown on Jerusalem artichoke extract was investigated. With the free cells, the ethanol and biomass yields were relatively constant over the temperature range 25-35°C, but dropped sharply beyond 35°C. Other kinetic parameters, specific growth rate, specific ethanol production rate, and specific total sugar uptake rate were maximum at 35°C. However, with the immobilized cells, ethanol yield remained almost constant in the temperature range 25-45°C, and the specific ethanol production rate and specific total sugar uptake rate attained their maximum values at 40°C. For the pH range between 3 and 7, the free-cell optimum for growth and product formation was found to be ca. pH 5. At this pH, the specific growth rate was 0.35 h-1 and specific ethanol production rate was 2.83 g/g/h. At values higher or lower than pH 5, a sharp decrease in specific ethanol production rate as well as specific growth rate was observed. In comparison, the immobilized cells showed a broad optimum pH profile. The best ethanol production rates were observed between pH 4 and 6.
    Additional Material: 10 Ill.
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  • 84
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    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 29 (1987) 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
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  • 85
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    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 30 (1987), S. 565-570 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The feasibility of using specific enzyme and transport inhibitors to minimize the glutamine response of a potentiometric microbial sensor is demonstrated. The glutamine response of a bacterial electrode prepared with Escherichia coli as the biocatalyst in conjunction with an ammonia gas-sensing electrode was greatly reduced by treating the electrode with the enzyme inhibitor 6-diazo-5-oxo-L-norleucine (DONL) and the transport inhibitor γ-L-glutamylhydrazide. Each inhibitor effectively decreased glutamine response to a level sufficiently low to be considered negligible in clinical studies. Although the sensor ultimately recovered from the effects of a single exposure to an inhibitor, continuous exposure at an optimum concentration maintained a low response to glutamine. Furthermore, the treatment of the sensor with both inhibitors simultaneously resulted in a negligible response to glutamine of 〈1 mV, indicating that both inhibitors are necessary for optimum inhibition of glutamine response. This approach is promising as a means of enhancing the selectivity of microbial sensors.
    Additional Material: 1 Ill.
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  • 86
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    Biotechnology and Bioengineering 30 (1987), S. 325-328 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 2 Ill.
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  • 87
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    Biotechnology and Bioengineering 30 (1987), S. 329-330 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 2 Ill.
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  • 88
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    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 30 (1987) 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
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  • 89
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    Biotechnology and Bioengineering 30 (1987), S. 331-333 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 2 Ill.
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  • 90
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    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 30 (1987), S. 335-344 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An adaptive steady-state optimization algorithm is presented and applied to the problem of optimizing the production of biomass in continuous fermentation processes. The algorithm requires no modeling information but is based on an on-line identified linear model, locates the optimum dilution rate, and maintains the chemostat at its optimum operating condition at all times. The behavior of the algorithm is tested against a dynamic model of a chemostat that incorporates metabolic time delay, and it is shown that large disturbances in the subtrate feed concentration and the specific growth rate, causing a shift in the optimum, are handled well. The developed algorithm is also used to drive a methylotroph single-cell production process to its optimum.
    Additional Material: 4 Ill.
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  • 91
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    Biotechnology and Bioengineering 30 (1987), S. 345-347 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In gas-liquid dispersions based on viscous non-Newtonian fluids, numerous very small bubbles are formed due to their high residence times in contacting devices such as bubble columns. The influence of these small bubbles on the measurement of the volumetric mass transfer coefficient in the contactor by the dynamic CO2 gas analysis method is discussed. It is found that their effect on this measuring technique is insignificant compared to that when using the conventional dissolved-oxygen technique.
    Additional Material: 2 Tab.
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  • 92
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    Biotechnology and Bioengineering 30 (1987), S. 348-351 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Distribution coefficients and selectivities of a number of mixed solvent systems have been determined in order to assess their suitability in preferentially extracting ethanol from aqueous solution. The measured values of distribution coefficients and selectivities differ substantially from the values estimated by interpolating between the pure solvents.
    Additional Material: 5 Tab.
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  • 93
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    Biotechnology and Bioengineering 30 (1987), S. 363-367 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Amylase synthesis by the yeasts Saccharomycopsis fibuligera and Schwanniomyces castellii and alluvius is repressed by glucose. Steady state continuous culture data for amylase activity, E, biomass concentration, X, and reducing sugar concentration, S, were fitted to the three-parameter catabolite repression model \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{E}{X} = \frac{{[1 + a(S/X)]}}{{[1 + b(S/X)]}}, $\end{document} and biomass productivity, DX, and amylase productivity, DE, were determined for S. castellii and S. alluvius.
    Additional Material: 7 Ill.
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  • 94
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The changes in growth kinetics in aerobic batch cultures of Klebsiella pneumoniae were followed by measurements of extracellular metabolites, rates of gas exchange, dissolved oxygen tension, pH, and carbon balance at all stages of growth. When the initial growth-limiting glucose concentration in media without pH control was increased from 1.0 g carbon L-1 to 2.2 g carbon L-1, the number of different, mainly acidic, extracellular metabolites of glucose at the end of exponential growth increased, while the proportion of acetate decreased. During the postexponential growth phase, the extracellular metabolites were oxidized, resulting in an increasing complexity of changes in pH, gas exchange, and dissolved oxygen tension with increasing initial substrate concentration. All these parameters showed concomitant stepwise changes. This pattern was independent of the dissolved oxygen tension in the range 30-200 μM. When pH was kept constant, the number, slope, and relative magnitude of the steps in gas exchange and dissolved oxygen tension were pH-dependent, being most complex at low pH. Detailed carbon balances showed that 20% of the initial glucose was converted into extracellular metabolites at the end of exponential growth at neutral pH. In the postexponential phase, pyruvate (2%) was reoxidized first followed by acetate (13%). The observed molar growth yield coefficient (YATP) was 8.4 if the transitory occurrence of pyruvate and acetate was accounted for, and 6.4 if it was neglected. The corrected observed molar growth yield coefficient (Y′ATP) was 9.4 and compared well with the true molar growth yield coefficient (YMaxATP), which was found to be 11.0. Specific in situ respiration rates of the exponential growth phase of cultures grown at different controlled pH values compared well with in situ values for energy-limited chemostat grown cells at the same growth rates, suggesting that growth in the batch culture was energy-limited throughout the exponential growth phase. This view was supported by low levels of intracellular glycogen and exopolysaccharides of all cultures, by the value of Y′ATP of 9.4, and by a constant specific production rate of the extracellular metabolites throughout exponential growth. It was concluded that even under strictly aerobic conditions, control of pH is as important as control of dissolved oxygen tension during growth of enterobacteriaceae in batch cultures.
    Additional Material: 4 Ill.
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  • 95
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    Biotechnology and Bioengineering 30 (1987), S. 368-373 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Both kLa and kL measurements were carried out by an unsteady state technique at impeller speeds ranging from 1.6 to 5.8 s-1 in a mechanically agitated animal cell culture vessel of working volume 1.5 L. Checks were made that the time constant of the oxygen electrode was negligible compared to the time for aeration and that the oxygen electrode reading was not a function of agitator speed in the range employed. The kL values by surface aeration of (1.18-3.54) × 10-5 m/s and kLa values by sparged aeration of (2.8-8.5) × 10-4 s-1 were found. The former are in reasonable agreement with published experimental values and the latter in accord with values estimated from published correlations based on agitator power input and aeration rate. The fluids used were water, basal medium, and basal medium supplemented with 5% (v/v) foetal calf serum; for each of these, kL and kLa values were similar. However, the addition of silicone antifoam (6 PPM) reduced the kLa value by ca. 50%.
    Additional Material: 5 Ill.
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  • 96
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    Biotechnology and Bioengineering 30 (1987), S. 374-380 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The kinetics of the hydrolysis of soluble starch by simultaneous use of β-amylase and either isoamylase or pullulanse was studied experimentally for a wide range of subtrate and enzyme concentrations. A kinetic expression was constituted for maltose production by β-armylase, which was stimulated by an increase in linear linkage portions due to the debranching enzyme on amylopectin molecules. As a result, calculations by the kinetic expression agreed with time course data under various conditions.
    Additional Material: 10 Ill.
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  • 97
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    Biotechnology and Bioengineering 30 (1987), S. 381-388 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The effect of water on equilibria for hydrolytic reaction in reversed micelles has been investigated using lipase as a model enzyme. The effect of water on equilibria has been ignored for hydrolase reactions in an aqueous phase. In a reversed micellar system, however, the equilibrium of the lipase reaction was changed when water was added during the hydrolytic reaction. Furthermore, equilibrium fractional conversion is affected by the initial water concentration, being shifted to higher values with higher water concentrations, with other reaction conditions being held constant, indicating that the reaction should be regarded as a two-substrate process. Equations corresponding to a two-substrate, second-order reversible model are derived and used for further analysis. The progress curves predicted from the rate equations agree very well with the experimental results under various reaction conditions. The values of the molar ratio of water to surfactant (R) which maximize the initial reaction rate and maximum fractional conversion is predictable from the derived rate equations and the resulting relationship between R and the kinetic constants.
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  • 98
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    Biotechnology and Bioengineering 30 (1987), S. 389-397 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The design of bioreactors for genetically modified bacterial cultures would benefit from predictive models. Of particular importance is the interaction of the external environment, cell physiology, and control of plasmid copy number. We have recently developed a model based on the molecular mechanisms for control of replication of Co1E1 type plasmids. The inclusion of the plasmid model into a single-cell E. coli model allows the explicit prediction of the interaction of cell physiology and plasmid-encoded functions. The model predictions of the copy number of plasmids with the Co1E1 origin of replication carrying a variety of regulatory mutations is very close to that observed experimentally.All of the model parameters for plasmid replication control can be obtained independently and no adjustable parameters are needed for the plasmid model. In this article we discuss the model's use in predicting the effect of operating conditions on production of a protein from a plasmid encoded gene and the stability of the recombinant cells in a continuous culture.
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  • 99
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    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 30 (1987), S. 628-637 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This article describes the synthesis and regulation of β(1-3)glucanase and protease enzymes from the cell lytic system of Oerskovia xanthineolytica LL-G109 in continuous culture using different concentrations of carbon source (glucose) and inducer (glucan). These two enzyme activities are the main components of a lytic system capable of lysing and disrupting whole yeast cells; it is subject to catabolite repression by glucose and is induced by yeast glucan. Peaks of β(1-3)glucanase and protease activity are obtained at dilution rates of between 0.05 and 0.15 h-1. The glucanase-protease ratio is very high compared to other strains. At dilution rates above 0.15 h-1 all activities are similar to those obtained in batch culture. The lytic enzyme system appears to contain several β(1-3)glucanase enzymes. In continuous culture both productivity and enzyme concentrations are greatly in creased when compared to batch culture, 11- and 4.4-fold, respectively.
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  • 100
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    Biotechnology and Bioengineering 30 (1987), S. 638-649 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A mathematical model that describes the dynamic behavior of the elution stage of biospecific adsorption (affinity chromatography) in a fixed bed is developed and solved. Both non-selective and selective elution methods are considered. The results show that the duration of the elution stage for a given bed length decreases as the value of the Porath parameter for elution increases. The concentrating effect of the elution stage on the adsorbate of interest increases as the bed length and the value of the Porath parameter for elution increase. It is shown that it is inappropriate to assume that the eluent is infinitely fast distributed within the pores of the particles, and an interesting result involving a local maximum in the effluent concentration of the selective eluent is obtained when the direction of flow in the elution stage is the same as in the adsorption and wash stages and the bed length is large. When the direction of flow during elution is opposite (as compared to being the same) to that employed in the adsorption and wash stages, a shorter total elution time is obtained. The advantage gained with a reversed flow increases as the bed length decreases.
    Additional Material: 7 Ill.
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