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  • 101
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 9 (1991), S. 99-107 
    ISSN: 0887-3585
    Schlagwort(e): protein structure ; hydrogen bonding ; interactions of side chains ; cysteine ; methionine ; half-cystine ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin
    Notizen: Intrachain hydrogen bonds are a hallmark of globular proteins. Traditionally, these involve oxygen and nitrogen atoms. The electronic structure of sulfur is compatible with hydrogen bond formation as well. We surveyed a set of 85 high-resolution protein structures in order to evaluate the prevalence and geometry of sulfur-containing hydrogen bonds. This information should be of interest to experimentalists and theoreticians intersted in protein structure and protein engineering.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 102
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 9 (1991), S. 90-98 
    ISSN: 0887-3585
    Schlagwort(e): calorimetry ; unfolding of protein ; CD spectra ; denaturation by guanidine hydrochloride ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin
    Notizen: To study the role of Pro residues in the conformation and conformational stability of a protein, nine mutant α subunits of tryptophan synthase from Escherichia coli, in which Ala or Gly was substituted for each of six Pro residues (positions 28, 57, 62, 96, 132, and 207) that are conserved in 10 microoganisms, were constructed by means of site-directed mutagenesis. The far-ultraviolet (UV) CD spectra of five mutant α subunits with Ala in place of Pro were identical to the spectrum of the wild-type protein, the exception being the mutant at position 207 (P207A). CD values in the far-UV region were less negative for P207A, indicating that the Pro residue at position 207 plays a role in maintaining the intact structure of the α subunit. The negative CD values of the Gly mutants examined (P28G, P96G, and P132G) were also decreased. Calorimetric measurements showed that the two mutants at position 28 (P28G and P28A) gave two peaks in the excess heat capacity curve, whereas the wild type and other Pro mutants had only a single peak. The stability of each mutant protein relative to that of the wild type was about the same for P57A, less for P62A and P132A, and markedly decreased for P96A and P207A, which are substituted at less mobile positions. The changes of denaturation entropy (ΔΔdS) at the denaturation temperature of the wild-type protein (54.1 °C at pH 9.0) were positive for P57A, P62A, and P132A, but negative for P96A, P207A, and P132G. The present results do not indicate that the differences in stability (ΔdG) among Pro substitutions are caused only by an entropic factor, as might be theoretically expected. The decreases in stability for P96A and P207 were due to the considerable decrease in denaturation enthalpy, although they were partly compensated for by the decrease in entropy. Our results also suggest that Pro-28 stabilizes the interaction between two domains of the α subunit.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 103
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 9 (1991), S. 120-134 
    ISSN: 0887-3585
    Schlagwort(e): plasmid SSBs ; protein and DNA sequence ; single-stranded DNA binding proteins ; helix destabilizing proteins ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin
    Notizen: The DNA and protein sequences of single-stranded DNA binding proteins (SSBs) encoded by the plP71a, plP231a, and R64 conjugative plasmids have been determined and compared to Escherichia coli SSB and the SSB encoded by F-plasmid. Although the amino acid sequences of all of these proteins are highly conserved within the NH2-terminal two-thirds of the protein, they diverge in the COOH-terminal third region. A number of amino acid residues which have previously been implicated as being either directly or indirectly involved in DNA binding are conserved in all of these SSBs. These residues include Trp-40, Trp-54, Trp-88, His-55, and Phe-60. On the basis of these sequence comparisons and DNA binding studies, a role for Tyr-70 in DNA binding is suggested for the first time. Although the COOH-terminal third of these proteins diverges more than their NH2-terminal regions, the COOH-terminal five amino acid residues of all five of these proteins are identical. In addition, all of these proteins share the characteristic property of having a protease resistant, NH2-terminal core and an acidic COOH-terminal region. Despite the high degree of sequence homology among the plasmid SSB proteins, the F-plasmid SSB appears unique in that it was the only SSB tested that neither bound well to poly(dA) nor was able to stimulate DNA polymerase III holoenzyme elongation rates. Poly [d(A-T)] melting studies suggest that at least three of the plasmid encoded SSBs are better helix-destabilizing proteins than is the E. coli SSB protein.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 104
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 9 (1991), S. 225-227 
    ISSN: 0887-3585
    Schlagwort(e): protein crystals ; crystallography ; latency ; tissue plasminogen activator ; N-terminal ; methionine ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin
    Notizen: Crystals of bacterially expressed plasminogen activator inhibitor (PAI-1) suitable for X-ray diffraction analysis have been obtained from 8% (w/v) PEG 1500, pH 8.25. The space group is P1, and the lattice constants are a = 82.17 Å, b = 47.82 Å, c = 62.89 Å, α = 90.00°, β = 106.90°, γ = 106.84°. The diffraction limit is 2.3 Å, and the unit cell contains two molecules of PAI-1. The crystals contain latent PAI-1 which can be partly reactivated by exposure to denaturants.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 105
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 10-21 
    ISSN: 0887-3585
    Schlagwort(e): electrostatics ; salt bridge ; thermal factor ; cysteine ; disulfide ; protein crystallography ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin
    Notizen: Crystals of bacteriophage T4 lysozyme used for structural studies are routinely grown from concentrated phosphate solutions. It has been found that crystals in the same space group can also be grown from solutions containing 0.05 M imidazole chloride, 0.4 M sodium choride, and 30% polyethylene glycol 3500. These crystals, in addition, can also be equilibrated with a similar mother liquor in which the sodium chloride concentration is reduced to 0.025 M. The availability of these three crystal variants has permitted the structure of T4 lysozyme to be compared at low, medium, and high ionic strength. At the same time the X-ray structure of phage T4 lysozyme crystallized from phosphate solutions has been further refined against a new and improved X-ray diffraction data set.The structures of T4 lysozyme in the crystals grown with polyethylene glycol as a precipitant, regardless of the sodium chloride concentration, were very similar to the structure in crystals grown from concentrated phosphate solutions. The main differences are related to the formation of mixed disulfides between cysteine residues 54 and 97 and 2-mercaptoethanol, rather than to the differences in the salt concentration in the crystal mother liquor. Formation of the mixed disulfide at residue 54 resulted in the displacement of Arg-52 and the disruption of the salt bridge between this residue and Glu-62.Other than this change, no obvious alterations in existing salt bridges in T4 lysozyme were observed. Neither did the reduction in the ionic strength of the mother liquor result in the formation of new salt bridge interactions. These results are consistent with the ideas that a crystal structure determined at high salt concentrations is a good representation of the structure at lower ionic strengths, and that models of electrostatic interactions in proteins that are based on crystal structures determined at high salt concentrations are likely to be relevant at physiological ionic strengths.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 106
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991) 
    ISSN: 0887-3585
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin
    Materialart: Digitale Medien
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  • 107
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 70-80 
    ISSN: 0887-3585
    Schlagwort(e): locally enhanced sampling ; molecular dynamics ; ligand penetration ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin
    Notizen: The thermally assisted diffusion of a small ligand (carbon monoxide) through a protein matrix (lupine leghemoglobin) is investigated computationally. The diffusion paths are calculated by a varient of the time-dependent Hartree approximation which we call LES (locally enhanced sampling). The variant which was recently introduced by Elber and Karplus1 is based on the classical TD-SCF approximation of Gerber et al.2 The simulation enables more significant search for diffusion pathways than was possible before. This is done by increasing the number of ligand trajectories using a single trajectory for the protein. We compare qualitatively diffusion rates in leghemoglobin and in myoglobin. The calculation shows that the diffusion in leghemoglobin is much faster than the diffusion in myoglobin, in agreement with experiment. The gate in leghemoglobin is opened by fluctuations at a close contact between the B/C and the G helices. The most relevant fluctuation is the rigid shift of the C helix with respect to the G helix. This path is not observed in a comparable calculation for myoglobin.1 This finding is rationalized by the lack of the D helix in leghemoglobin and a significantly more flexible CE loop. Supporting experimental evidence for the importance of the CE loop in leghemoglobin can be found in the kinetics studies of Gibson et al.28
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 108
    ISSN: 0887-3585
    Schlagwort(e): aspartyl protease ; HIV-1 and -2 proteases ; calmodulin ; specificity ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin
    Notizen: Calcium-free calmodulin-(CaM) is rapidly hydrolyzed by proteases from both human immunodeficiency viruses (HIV) 1 and 2. Kinetic analysis reveals a sequential order of cleavage by both proteases which initiates in regions of the molecule known from X-ray crystallographic analysis of Ca2+/CaM to be associated with calcium binding. Although HIV-1 and HIV-2 proteases hydrolyze two bonds in common, the initial site of cleavage required for subsequent events differs in each case. The first bond hydrolyzed by the HIV-1 protease in the Asn-Tyr linkage in the sequence,-N-I-D-G-D-G-Q-V-N-Y-E-E, found in the fourth calcium binding loop. In contrast, it is an Ala-Ala bond in the third calcium loop, -D-K-D-G-N-G-Y-I-S-A-A-E-, that is first hydrolyzed by the HIV-2 enzyme, followed in short order by cleavage of the same Asn-Tyr linkage described above. Thereafter, both enzymes proceed to hydrolyze additional peptide bonds, some in common, some not. Considerable evidence exists that inhibitors are bound to the protease in an extended conformation and yet all of the cleavages we observed occur within, or at the beginning of helices in Ca2+/CaM, regions that also appear to be insufficiently exposed for protease binding. Molecular modeling studies indicate that CaM in solution must adopt a conformation in which the first cleavage site observed for each enzyme is unshielded and extended, and that subsequent cleavages involve further unwinding of helices. The conclusion that the conformation of CaM is different from that of Ca2+/CaM is supported by the observation that Ca2+/CaM is resistant to hydrolysis by either enzyme. As well as demonstrating conformational differences between CaM and Ca2+/CaM, these studies provide further evidence that the two highly homologous human retroviral proteases may be distinguished enzymologically in terms of differential substrate specificities. In addition, some new and unpredicted sequences have been identified that undergo cleavage by these enzymes. Finally, the fact that an abundant, ubiquitous, and biologically important cellular protein is broken down by the HIV proteases could be physiologically relevant to HIV infection if the viral enzyme ever displays activity within the host cell.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 109
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 251-259 
    ISSN: 0887-3585
    Schlagwort(e): Ricin A-chain ; x-ray structure ; active site ; conserved residues ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin
    Notizen: Ricin has been refined in a crystallographic sense to 2.5 Å resolution and the model for the A-chain (RTA) is described in detail. Because RTA is the first member of the class of plant toxins to be analyzed, this model probably defines the major structural characteristics of the entire family of these medically important proteins. Explanations are provided to rationalize amino acids that are conserved between RTA and a number of homologous plant and bacterial toxins. Eight invariant residues appear to be involved in creating or stabilizing the active site. In the active site Arg180 and Glu177 are hydrogen bonded to each other and also coordinate a water molecule; each of these groups may be important in the N-glycosidation reaction. Several other polar residues may play lesser roles in the mechanism, including tyrosines 80 and 123 and asparagines 78 and 209. A number of conserved hydrophobic residues are seen to cluster within several patches and probably drive the overall folding of the toxin molecule.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 110
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 270-278 
    ISSN: 0887-3585
    Schlagwort(e): ricin A ; site-directed mutagenesis ; mechanism of action ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin
    Notizen: Ricin A-chain is an N-glycosidase that attacks ribosomal RNA at a highly conserved adenine residue. The enzyme is representative of a large family of medically significant proteins used in the design of anticancer agents and in the treatment of HIV infection. The x-ray structure has been used as a guide to create several active site mutations by directed mutagenesis of the cloned gene. Glu177 is a key catalytic residue, and conversion to Gln reduces activity 180-fold. Asn209 is shown to participate in substrate binding by kinetic analysis. Conversion to Ser increases Km sixfold but has no effect on kcat. Conversion of Tyr80 and Tyr123 to Phe decreases activity by 15- and 7-fold respectively. A mechanism of action is proposed that involves binding of the substrate adenine in a syn configuration that resembles the transition state; the putative oxycarbonium ion is probably stabilized by interaction with Glu177.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 111
    ISSN: 0887-3585
    Schlagwort(e): site-directed mutagenesis ; cysteine ; phosphoglycerate kinase ; IAEDANS ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin
    Notizen: The effects of ligands on the conformation of yeast phosphoglycerate kinase were explored by introducing cysteinyl residues at different positions in the molecule by site-directed mutagenesis. Thus several mutants were constructed, each containing a unique cysteinyl residue. Neither the conformation nor the enzyme activity was affected by the substitutions. The reactivity of the thiol groups and the fluorescence of N-acetyl-N′-(5-sulfo-1-naphtyl)ethylene-diamine covalently linked to these thiols were used to monitor the conformational changes induced upon ligand binding.It was found that the observed changes mainly involve the part of the protein located in the cleft, particularly the environment of residues 35 and 183. No alteration was observed on the external side of the protein. Only 3-Phosphoglycerate induced these conformational changes. However, when the fluorescent probe was attached to residue 377, the binding of the two substrates was required to induce a modification in the fluorescence of the probe. These results indicate that the substrates separately or together induce discrete molecular motions in phosphoglycerate kinase.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 112
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 10 (1991), S. 359-359 
    ISSN: 0887-3585
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin
    Materialart: Digitale Medien
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  • 113
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 11 (1991), S. 1-12 
    ISSN: 0887-3585
    Schlagwort(e): electrostatics ; enzyme-substrate interaction ; solvent screening ; active site potential ; structure-function relationship ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin
    Notizen: Escherichia coli dihydrofolate reductase (DHFR) carries a net charge of -10 electrons yet it binds ligands with net charges of -4 (NADPH) and -2 (folate or dihydrofolate). Evaluation and analysis of the electrostatic potential of the enzyme give insight as to how this is accomplished. The results show that the enzyme is covered by an overall negative potential (as expected) except for the ligand binding sites, which are located inside “pockets” of positive potential that enable the enzyme to bind the negatively charged ligands. The electrostatic potential can be related to the asymmetric distribution of charged residues in the enzyme.The asymmetric charge distribution, along with the dielectric boundary that occurs at the solvent-protein interface, is analogous to the situation occurring in superoxide dismutase. Thus DHFR is another case where the shape of the active site focuses electric fields out into solution.The positive electrostatic potential at the entrance of the ligand binding site in E. coli DHFR is shown to be a direct consequence of the presence of three positively charged residues at positions 32, 52, and 57-residues which have also been shown recently to contribute significantly to electronic polarization of the ligand folate. The latter has been postulated to be involved in the catalytic process. A similar structural motif of three positively charged amino acids that gives rise to a positive potential at the entrance to the active site is also found in DHFR from chicken liver, and is suggested to be a common feature in DHFRs from many species. It is noted that, although the net charges of DHFRs from different species vary from +3 to -10, the enzymes are able to bind the same negatively charged ligands, and perform the same catalytic function.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 114
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 11 (1991), S. 77-77 
    ISSN: 0887-3585
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin
    Materialart: Digitale Medien
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  • 115
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 11 (1991), S. 59-76 
    ISSN: 0887-3585
    Schlagwort(e): protein structure ; amino acid sequence ; database ; macromolecules ; molecular modeling ; knowledge base ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin
    Notizen: A system is described that provides ways of integrating data on protein structure, sequence, and survey results, with molecular graphics and molecular mechanics software. Its major component is the relational database SESAM, presently implemented under the commercial package SYBASE. By desin, the database allows full integration - within the same data organization - of raw data on protein structure, sequence, ligands, and heterogroups, obtained from the Brookhaven Protein Databank, with pure sequence information available from other databanks such as SWISS-PROT. It contains in addition higher level descriptions of structural and topological properties, as well as survey results, obtained by executing specialized computer programs. Aside from the very useful attribute of closely combining structural and nonstructural information, other important features distinguish it from analogous systems developed elsewhere. It includes a molecular dictionary with complete description of geometric properties and energy parameters used in modeling and conformational energy calculations. Using this dictionary, structural data are validated by checking for localized inconsistencies in atomic coordinates, atomic symbols, chirality definitions, and flagging errors and incomplete entries. Because of both the dictionary and the validation procedures, SESAM can be readily interfaced with conventional molecular graphics and mechanics software packages, or with other specialized application programs. With the aid of appropriate interfaces, data access is sufficiently fast for SESAM to be interrogated interactively. Prototypes of user interfaces, as well as an interface with the molecular graphics package BRUGEL, are described and the power of the system is illustrated in applications such as homology-based protein modeling, computer-aided protein design, protein structure predictions, analysis of local structure motifs, and of relationships between protein sequence and structure.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 116
    ISSN: 0887-3585
    Schlagwort(e): anti-ss-DNA autoantibody ; deoxynucleotide-Fab complex ; conformational changes in protein when ligand is bound ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin
    Notizen: Crystal structures of the Fabs from an autoantibody (BV04-01) with specificity for single-stranded DNA have been determined in the presence and absence of a trinucleotide of deoxythymidylic acid, d(pT)3. Formation of the ligand-protein complex was accompanied by small adjustments in the orientations of the variable (VL and VH) domains. In addition, there were local conformational changes in the first hypervariable loop of the light chain and the third hypervariable loop of the heavy chain, which together with the domain shifts led to an improvement in the complementarity of nucleotide and Fab. The sugar-phosphate chain adopted an extended and “open” conformation, with the base, sugar, and phosphate components available for interactions with the protein. Nucleotide 1 (5′-end) was associated exclusively with the heavy chain, nucleotide 2 was shared by both heavy and light chains, and nucleotide 3 was bound by the light chain. The orientation of phosphate 1 was stabilized by hydrogen bonds with serine H52a and asparagine H53. Phosphate 2 formed an ion pair with arginine H52, but no other charge-charge interactions were observed. Insertion of the side chain of histidine L27d between nucleotides 2 and 3 resulted in a bend in the sugar-phosphate chain. The most dominant contacts with the protein involved the central thymine base, which was immobilized by cooperative stacking and hydrogen bonding interactions. This base was intercalated between a tryptophan ring (no. H100a) from the heavy chain and a tyrosine ring (no. L32) from the light chain. The resulting orientation of thymine was favorable for the simultaneous formation of two hydrogen bonds with the backbone carbonyl oxygen and the side chain hydroxyl group of serine L91 (the thymine atoms were the hydrogen on nitrogen 3 and keto oxygen 4).
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 117
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 11 (1991) 
    ISSN: 0887-3585
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin
    Materialart: Digitale Medien
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  • 118
    ISSN: 0887-3585
    Schlagwort(e): protein-ligand interactions ; electrostatics ; density functional theory ; protein structure-function relationship ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin
    Notizen: Quantum-mechanical electron density calculations reveal that a significant polarization is induced in the cofactor NADPH (reduced nicotinamide adenine dinucleotide phosphate) on binding to the enzyme dihydrofolate reductase. The calculations indicate that electron density corresponding to ∼0.7 electron charges is shifted within the molecule, extending over more than 20Å. Further calculations on proposed enzyme mutants show that the polarization of NADPH on binding to DHFR is, in large part, induced by a motif of three positively charged residues. This motif was also identified to be directly responsible for the positive electrostatic potential surrounding the cofactor binding site in the enzyme. The possibility of this long-range polarization of NADPH was originally proposed based on a previous study of ligand binding to DHFR where a conserved structural motif of three positively charged residues was found to play a major role in polarizing the substrate folate over its entire length of 18 Å.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 119
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 11 (1991), S. 218-222 
    ISSN: 0887-3585
    Schlagwort(e): antibody ; Fab ; antigen ; crystallization ; x-ray crystallography ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin
    Notizen: TE33 is an Fab fragment of a monoclonal antibody raised against a 15-residue long peptide (CTP3), corresponding in sequence to residues 50-64 of the cholera toxin B subunit. Crystals of the complex between TE33 and CTP3 have been grown from 20% (w/v) polyethylene glycol-8000 at pH 4.0. The crystals are orthorhombic, space group P21212, with unit cell dimensions a = 104.15, b = 110.61, and c = 40.68 Å. X-Ray data have been collected to a resolution of 2.3 Å. The asymmetric unit contains one molecule of Fab and one molecule of CTP3. The presence of CTP3 has been demonstrated by fluorescence quenching of the dissolved crystal after X-ray data collection. A molecular replacement solution was found based on the coordinates of DB3, an antiprogesterone Fab fragment.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 120
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 11 (1991), S. 237-237 
    ISSN: 0887-3585
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin
    Materialart: Digitale Medien
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  • 121
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 11 (1991), S. 239-241 
    ISSN: 0887-3585
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin
    Materialart: Digitale Medien
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  • 122
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 11 (1991), S. 254-262 
    ISSN: 0887-3585
    Schlagwort(e): EPR ; molecularity ; colicin E1 ; ion channel ; kinetics ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin
    Notizen: The molecularity of the ion channel formed by peptide fragments of colicin has taken on particular significance since the length of the active peptide has been shown to be less than 90 amino acids and the lumen size at least 8 Å. Cell survival experiments show that killing by colicin obeys single-hit statistics, and ion leakage rates from phospholipid vesicles are first order in colicin concentration. However, interpretation in molecular terms is generally complicated by the requirement of large numbers of colicin molecules per cell or vesicle.We have measured the discharge of potential across membranes of small phospholipid vesicles by following the changes in binding of potential sensitive spin labeled phosphonium ions as a function of the number of colicin fragments added. Because of the sensitivity of the method, it was possible to reliably investigate the effect of colicin in a range where there was no more than 0.2 colicins per vesicle. The quantitative results of these experiments yield a direct molecular stoichiometry and demonstrate that one C-terminal fragment of the colicin molecule per one vesicle is sufficient to induce a rapid ion flux in these vesicles. In addition, the experiments confirm earlier findings that the colicin fragments do not migrate from one vesicle to another at pH 4.5. Similar results are obtained with large unilamellar vesicles.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 123
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 11 (1991), S. 297-313 
    ISSN: 0887-3585
    Schlagwort(e): information theory ; entropy ; variability ; sequence comparison ; immunoglobulins ; antibodies ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin
    Notizen: We propose the use of the information-theoretical entropy, S = -Σpi log2 Pi, as a measure of variability at a given position in a set of aligned sequences. pi stands for the fraction of times the i-th type appears at a position. For protein sequences, the sum has up to 20 terms, for nucleotide sequences, up to 4 terms, and for codon sequences, up to 61 terms. We compare S and VS, a related measure, in detail with VK, the traditional measure of immunoglobulin sequence variability, both in the abstract and as applied to the immunoglobulins. We conclude that S has desirable mathematical properties that VK lacks and has intuitive and statistical meanings that accord well with the notion of variability. We find that VK and the S-based measures are highly correlated for the immunoglobulins. We show by analysis of sequence data and by means of a mathematical model that this correlation is due to a strong tendency for the frequency of occurrence of amino acid types at a given position to be log-linear. It is not known whether the immunoglobulins are typical or atypical of protein families in this regard, nor is the origin of the observed rank-frequency distribution obvious, although we discuss several possible etiologies.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 124
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991) 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 125
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 17-25 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Bacterial biofilm removal processes due to shear and catastrophic sloughing have been investigated in a turbulent flow system under conditions of carbon versus oxygen substrate limitations and varying aqueous phase calcium concentrations. Biofilm cellular and extracellular polymer carbon, total biofilm carbon and mass, and biofilm calcium concentrations are measured for pure culture biofilms of the facultative aerobe, Pseudomonas putida ATCC 11172. Results indicate oxygen-limited biofilms reach a higher steady-state biofilm organic carbon level than carbon-limited biofilms. Oxygen-limited biofilms also exhibit (1) a higher extracellular polymer-carbon: cell-carbon ratio throughout biofilm development and (2) a higher biofilm calcium content than carbon-limited biofilms. Increasing aqueous phase calcium concentrations increase the amount of biofilm calcium in both cases; the rate of calcium accumulation in oxygen-limited biofilms increases with increasing liquid phase calcium concentrations over the entire range studied while the rates of calcium accumulation in carbon-limited biofilms appear independent of aqueous phase calcium concentrations above 11.0 mg/L. Oxygen-limited biofilms with their higher extracellular polymer and calcium content exhibit shear removal rates that are 20-40% of those observed for carbon-limited biofilms. However, it is the oxygen-limited biofilms that experience catastrophic sloughing events. The carbon-limited biofilms studied here never sloughed even if subjected to intentional long-term deprivation of all nutrients. Reduced shear removal and the susceptibility to sloughing of the oxygen-limited biofilms are attributed to their more cohesive structure bought about by their relatively greater extracellular polymer production.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 126
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 491-496 
    ISSN: 0006-3592
    Schlagwort(e): potentiostatic control of enzyme activity ; immobilized enzyme ; graphite ; conducting support ; specific anion inhibition ; carbonic anhydrase ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The effect of both a positive and a negative applied potential on the p-NPA hydrolysis activity of bovine carbonic anhydrase (BCA) immobilized on graphite rods has been investigated. Background experiments show that the pH-activity profile for BCA free in solution is not affected by either a negative or a positive potential applied to graphite rods placed in the same solution. However, the activity of BCA immobilized by covalent attachment to a graphite rod is influenced by a potential externally applied to the graphite rod. An overall increase in activity (as determined by the initial rate of the p-NPA hydrolysis reaction) is observed in the presence of a -0.2 V (Ag/AgCl) applied potential, while decreased activity is evident at +0.6 V (Ag/AgCl). This is indicative of an electrolyte anion effect rather than a local pH effect. In the presence of the specific anion inhibitors Cl- and SCN-, the relative BCA activity increases at -0.2 V (Ag/AgCl) and decreases at +0.6 V (Ag/AgCl) are consistent with the different BCA inhibition constants for Cl- and SCN-. Accelerated loss of immobilized BCA activity also accompanies the application of the external potentials, particularly at +0.6 V (Ag/AgCl). Results described here represent an early example of potentiostatic control of nonredox enzyme activity. Several possible mechanisms are discussed including specific anion inhibition, enzyme surface charge/charged support material interactions, and charged product inhibition. It is likely that a combination of such mechanisms is operational in this system. The implications of external potentials affecting the activity of immobilized enzymes in the design of stable immobilized enzyme electrodes are also discussed.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 127
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 528-536 
    ISSN: 0006-3592
    Schlagwort(e): yeast thermotolerance ; Saccharomyces ; invertase ; sugarcane juice fermentation ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Maintenance of high cell viability was the main characteristic of our new strains of thermotolerant Saccharomyces. Total sugar conversion to ethanol was observed for sugarcane juice fermentation at 38-40°C in less than 10 h and without continuous aeration of the culture. Invertase activity differed among the selected strains and increased during fermentation but was not dependent on cell viability. Invertase activity of the cells and optimum temperature for growth, as well as velocity of ethanol formation, were dependent on medium composition and the type of strain used. At high sugarcane syrup concentrations, the best temperature for ethanol formation by strain 781 was 35°C. Distinct differences among the velocities of ethanol production using selected strains were also observed in sugarcane syrup at 35-38°C.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
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  • 128
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991) 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 129
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 716-722 
    ISSN: 0006-3592
    Schlagwort(e): κ-carrageenan matrix ; Lactobacillus delbrueckii ; toxicity ; solvent diffusion ; extractive fermentation ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The toxicity of an Alamine 336/oleyl-alcohol extraction system on Lactobacillus delbrueckii was investigated. It was shown that the solvent affected the cells through the water-soluble portion and the immiscible portion of the solvent. While immobilization significantly protected the cells from the immiscible solvent phase, the water-soluble part of the solvent still caused toxicity to the microorganisms due to diffusion of the solvent into the matrix. Adding soybean oil to the κ-carrageenan matrix could trap the diffusing solvent molecules, and therefore reduce the toxic effect from the water soluble portion of the solvent. The protective ability of soybean oil was quantified through mathematical modeling and experimentation.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 130
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 746-754 
    ISSN: 0006-3592
    Schlagwort(e): Lactococcus cremoris ; cell-recycle fermentor ; cross-flow filtration ; high cell concentration cultures ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: High-cell concentration cultivation of Lactococcus cremoris, a homofermentative lactic acid producer, in a cell-recycle fermentor is described. Cross-flow filtration allowing continuous removal of the inhibitory metabollte, the influence of dilution rate on growth was investigated in total or partial cell-recycle cultures. The dependence of growth characteristics on operating conditions was identified and quantified using lactose as the carbon source. Growth kinetics could be described by both lactate removal efficiency and nutrient availability. Based on physiological observations, biomass and lactic acid productivities were predicted in partial cell-recycle cultures.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
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  • 131
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 778-789 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Biofilm research has focused on studies of undefined mixed microbial populations and, more recently, on investigations of monopopulation biofilms. In the first case, the biofilm is considered a homogeneous mass, ignoring the properties of individual species. The second case concentrates on the properties and processes of one microbial species in the biofilm. This article describes biofilm experiments conducted with monopopulations of Klebsiella pneumoniae and Pseudomonas aeruginosa and with binary populations of K. pneumoniae and P. aeruginosa. Process rates and stoichiometric coefficients were determined for the monopopulation and for the binary population biofilms and evaluated in light of the species distribution in the latter. Results indicate that neither the specific cellular product formation rate nor the glucose-oxygen stoichiometric ratio of K. pneumoniae or P. aeruginosa in the binary biofilm is affected by the presence of the other species. Consequently, species interaction was not observed. Although the specific cellular growth rate of K. pneumoniae is five times that of P. aeruginosa, the former species did not dominate the microbial population in the biofilm. Possible reasons for this unexpected behavior are discussed.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 132
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 802-808 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A simple structured model is described and compared with experimental data for fermentations with recombinant. Escherichia coli. The model is a so-called compartment, model, where the different biomass components are lumped together in a few intracellular variables. The model is able to describe, in a biologically reasonable fashion, a majority of the observations that have been made through fermentations with recombinant microorganisms. The model is especially suited for description of dynamic changes in plasmid copy number, e.g., runaway plasmid replication.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 133
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 834-842 
    ISSN: 0006-3592
    Schlagwort(e): microalgae ; bioreactor ; CO2 ; absorption ; KLa ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: For the characterization of CO2 absorption in aerated microalgal culture systems, a different approach based on KLa(O2) determination and transformation was studied. To confirm the validity of this method, the influence of reactions between CO2 and compounds (OH-, H2O, and NH3) present in the culture medium upon the absorption mechanism was evaluated under different physical and chemical culture conditions. Under these conditions, knowledge of the relative magnitudes of the diffusion and reaction kinetics permitted the evaluation of their relative importance. For the determination of the parameters required for the calculation of the CO2 absorption constant, empirical correlations for KL0 and a were used that had been previously verified with experimental data for O2 absorption. Since, for the conditions studied, the absorption rate was shown to be independent of the chemical reactions taking place in the liquid phase, the KLa for CO2 could be directly related to the KLa for O2 by a simple factor that took into account the difference in aqueous diffusivity of the two gases. Thus, using methods developed for determining O2 absorption in gas-liquid contactors, it is possible to adequately characterize CO2 absorption for laboratory and pilot scale algal production systems.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 134
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 883-888 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 135
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991) 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 136
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 918-921 
    ISSN: 0006-3592
    Schlagwort(e): plant cells ; photosynthesis ; microemulsion ; organic solvents ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: With the aim of possibly extending plant microbiology and photosynthesis beyond the usual applicability in aqueous solution, we investigated the solubilization of plant cells inorganic media with the help of water-in-oil microemulsions. Cells isolated from leaves of Rumex obtusifolius were solubilized in a water/2-ethyl-hexyl-sodiumsulfosuccinate/isooctane system, containing 20% water (v:v) and 240 mM surfactant, and the oxygen evolution/consumption was measured polarographically. Although no oxygen evolution was detectable in the organic medium, the cells were able to carry out photosynthetic oxygen consumption at the expense of ascorbate. To a lesser extent, photosynthetic oxygen consumption was measured using N, N, N′, N′-tetramethyl-p-phenylenediamine as electron donor. The rate of ascorbate photooxidation was linearly related to the concentration of cells.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 137
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The marine phytoplankter Tetraselmis suecica was grown in shallow outdoor flumes for a period of approximately 6 months at the Natural Energy Laboratory of Hawaii. In full sunlight, gross production rates were 15-20 g C m-2 d-1. The corresponding photosynthetic efficiencies (PE's) were 9-10%. Respiration losses removed about half the gross production. The CO2 utilization efficiencies of 96 ± 11% were achieved by bubbling CO2 into the culture with the use of a counterflow sump system. Adding the CO2 in the form of carbonated water resulted in utilization efficiencies of 81 ± 11%. Archimedes screws proved superior to both paddle wheels and propellers as a means of circulating the water in the flumes. Insertion of foil arrays into the flumes to effect systematic mixing of the culture significantly enhanced production. The enhancement was greater when the foils were oriented at a small angle relative to the horizontal than when they were oriented at the same angle relative to the vertical. Light modulation effects are implicated as the probable cause of most of the enhancement. Substitution of electric power plant stack gases for pure CO2 resulted in no significant change in the production of T. suecica grown in chemostat culture.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 138
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 967-972 
    ISSN: 0006-3592
    Schlagwort(e): papain ; organic solvent ; kinetics ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The effects of various concentrations of a water-miscible organic solvent [a 7:3 (v/v) mixture of N, N dimethylformamide and dimethylsulfoxide] on the kinetics of papain have been investigated. The parameters kcat and Km for the amidase and esterase activity of papain using N-α-benzoyl-DL-arginine-p-nitroanilide (BAPNA) and N-α-benzoyl-L-arginine ethyl ester (BAEE) as substrates were determined. For both types of activity, kcat initially increased (up to about 15% solvent), and then decreased with increasing concentrations of organic solvent. In contrast, Km increased sharply with the organic solvent concentration. Active site titration at 0 and 50% solvent indicated no change in the amount of active enzyme. Fluorometric measurements of the emission spectrum of papain did not indicate any major conformational changes with increasing concentrations of organic solvent.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 139
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 383-385 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 140
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 389-391 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Ethanol and cycloheximide inhibited the function of the ammonium transport system in growing cultures of Saccharomyces cerevisiae var. ellipsoideus measured as methylamine uptake. The effect was reversible with ethanol and irreversible with the antibiotic. The kinetic data are consistent with a reduction of the number of active carrier molecules located in the plasma membrane. In contrast, neither ethanol nor cycloheximide affected the specific rate of fructose uptake.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 141
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 397-403 
    ISSN: 0006-3592
    Schlagwort(e): immobilized Plant cells ; plant cells bioreactor ; Protoberberine Alkaloids ; Thalictrum rugosum ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Cultured Thalictrum rugosum cells were immobilized using a glass fiber substratum previously shown to provide optimum immobilization efficiency based on spontaneous adhesion mechanisms. When cultivated in shake flasks, immobilized cells exhibited decreased growth and protoberberine alkaloid production rates in comparison to freely suspended cells. Since alkaloid production is growth associated in T. rugosum, the decreased specific production rate was a function of the slower growth rate. Cells immobilized on glass fiber mats appear to be amenable for extended culture periods. Maximum biomass and protoberberine alkaloid levels were maintained for at least 14 days in immobilized cultures. In contrast, fresh weight, dry weight, and total alkaloid content decreased in suspension cultures following the linear growth phase.Glass fiber mats were incorporated in to a 4.5-L plant cell bioreactor as horizontal disks supported on a central rod. Mixing in the reactor was provided by the combined actions of a magnetic impeller and a cylindrical sparging colum. fThe magnetic impeller and a cylindrical sparging column. The entire inoculum biomass of T. rougosum, introduced as suspension, was spontaneously immobilized with in 8h. During liner phase, the growth rate of bioreactor cultivated immobilized cells (μ = 0.06 day-1) was 50% that immobilized cell viability in both systems was determined to be similar. The increase in specific production of protoberberine alklodis was initially similar in bioreactor-and culture period. The increase in specific production of protoberberine alkaloids was initially similar in bioreactor-and shake-flask-cultivated immobilized cells. However, the maximum specific production of bioreactor grown cultures was lower. The scale up potential of an immobilization strategy based on the spontaneous adhesion of immobilization strategy based on the spontaneous adhesion of cultured plant cells to glass fiber is demonstrated.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 142
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 190-195 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: No Abstrct.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 143
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 205-209 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The oxygen transfer characteristics of a 20-mm O.D. airlift contactor fitted with an oxygen microelectrode were determined by steady-state sulfite oxidation measurements. The volumetric mass transfer coefficient kLa was proportional to sparging power input per unit volume raised to a power which varied from 0.41 in water (coalescing bubbles) to 0.76 in NaCl solutions (noncoalescing bubbles). The highest observed kLa value was 0.012 s-1 which is sufficient to aerate Escherichia coli in an NMR spectrometer at moderate to high cell densities, depending on the physiological state of the cells.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 144
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 467-483 
    ISSN: 0006-3592
    Schlagwort(e): alkaline protease ; Bacillus firmus ; extracellular enzymes ; nitrogen/oxygen/phosphorous limitation ; acetic acid ; ethanol ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Proteolytic enzymes produced by Bacillus species find a wide variety of applications in brewing, detergent, food, and leather industries. Owing to significant differences normally observed in culture conditions promoting cell growth and those promoting production of metabolites such as enzymes, for increased efficacy of bioreactor operations it is essential to identify these sets of conditions (including medium formulation). This study is focused on formulation of a semidefined medium that substantially enhances synthesis and secretion of an alkaline protease in batch cultures of Bacillus firmus NRS 783, a known superior producer of this enzyme. The series of experiments conducted to identify culture conditions that lead to improved protease production also enables investigation of the regulatory effects of important culture parameters including pH, dissolved oxygen, and concentrations of nitrogen and phosphorous sources and yeast extract in the medium on cell growth, synthesis and secretion of protease, and production of two major nonbiomass products, viz., acetic acid and ethanol. Cell growth and formation of the three nonbiomass products are hampered significantly under nitrogen, phosphorous, or oxygen limitation, with the cells being unable to grow in an oxygen-free environment. Improvement in protease production is achieved with respect to each culture parameter, leading in the process to 80% enhancement in protease activity over that attained using media reported in the literature. Results of a few fed-batch experiments with constant feed rate, conducted to examine possible enhancement in protease production and to further investigate repression of protease synthesis by excess of the principal carbon and nitrogen sources, are also discussed. The detailed investigation of stimulatory and repressory effects of simple and complex nutrients on protease production and metabolism of Bacillus firmus conducted in this study will provide useful guidelines for design of bioreactors for production of protease and bulk chemicals by this bacterium.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 145
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 512-518 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Pseudomonas putida biofilms were developed on and biofilm accumulation rate data were obtained for the following two classes of support materials: charged surfaces and noncharged hydrophobic and hydrophilic surfaces. The effects of surface roughness and porosity on the rate of microbial attachment were also examined.Materials bearing a net positive or negative surface charge supported the greatest biofilm accumulation and the highest biofilm accumulation rate. Uncharged hydrophobic materials achieved the next greatest biofilm accumulation, averaging approximately 50% of the total biomass which was accumulated on the charged surface materials after 16 days. Uncharged hydrophilic materials supported very little biofilm development. In general, biofilm accumulation increased with decreased surface roughness. The effect of pore size on biofilm accumulation was not conclusive.The biofilm accumulation kinetics showed an exponential accumulation rate for the charged surfaces and an approximately linear accumulation rate for the hydrophobic materials. This difference in accumulation kinetics is consistent with proposed differences in the physicochemical mechanism governing attachment to these two types of surface materials.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 146
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 927-935 
    ISSN: 0006-3592
    Schlagwort(e): Bacillus subtilis ; recombinant plasmid ; deletion rate ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Recombinant plasmid pCEDS is structurally unstable in Bacillus subtilis cultures. We have previously shown that stability can be independently increased by changing from a complex medium supporting high growth rates to a chemically-defined medium supporting a lower growth rate and removal of a 4.77-kb EcoRI fragment from pCED3 to give plasmid YS1. Further stabilization was achieved by combining the two approaches. In the present work, we show that the stabilization of the plasmid-encoded LacZ+ phenotype can be explained solely by the effect on the growth rate ratio between cells containing modified and parental plasmids. By using modified stability experiments (where a single cell rather than a suspended colony was used to initiate growth), independent growth rate measurements, and a simple mathematical model, we can describe the kinetics of the loss of the LacZ+ phenotype in terms of two variables, α and p (where α is the ratio of growth rates between modified and parental cells, and p is the probability of obtaining modified cells from parental cells). Under the conditions tested, the average values of α were 1.52 for cultures growing in complex medium, 1.28 for cultures growing in defined medium, and 1.18 for cultures containing the modified plasmid pYS1 growing in complex medium. The calculated p values ranged between 10-8 and 10-10 under all conditions. Plasmid (pYS137) was used to directly estimate plasmid deletion rates in B. subtilis and it showed a rate between 5 × 10-8 and 1.1 × 10-9 deletions/cell/generation. In contrast to B. subtilis, there were no detectable differences in growth rates between Escherichia coli strains harboring plasmid pCEDS and plasmid-free cells. These results explain the observed stability of pCEDS in E. coli cultures and indicate that readily detected instability in B. subtilis cultures can be the result of rare deletion events.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 147
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 960-966 
    ISSN: 0006-3592
    Schlagwort(e): bioreactors ; oxygen transfer ; fermentation ; mycelial fermentation ; mass transfer ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The oxygen transfer in bioreactors with slurries having a yield stress was investigated. The volumetric mass transfer coefficients in a 40-L bubble column with simulated fermentation broths, the Theological properties of which were represented by the Casson model, were measured. Experimental data were compared with a theoretical correlation developed on the basis of a combination of Higbie's penetration theory and Kolmogoroff's theory of isotropic turbulence. Comparisons between the proposed correlation and data for the simulated broths show good agreement. The mass transfer data for actual mycelial fermentation broths reported previously by the authors were re-examined. Their Theological data was correlated by the Bingham plastic model. The oxygen transfer rate data in the mycelial fermentation broths fit the predictions of the proposed theoretical correlation.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 148
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 989-993 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 149
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 998-1003 
    ISSN: 0006-3592
    Schlagwort(e): Arthrobacter simplex ; controlled ultrasonic irradiation ; microbial conversion ; ultrasound facilitated diffusion ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Dehydrogenation of hydrocortisone by agitated suspensions of free and immobilized cells of Arthrobacter simplex ATCC 6946 was investigated under controlled ultrasonic irradiation at a frequency of 20 kHz. The microbial conversion was optimized first with respect to mechanical agitation and subsequently with respect to an additionally superimposed sonication. The optimization of ultrasound intensity and its mode of application were established at a level which maintained the structural integrity of the cells as well as their biocatalytic activity. Various regimes of ultrasound at power densities of 0.030-0.120 W/mL were applied in systems of soluble (0.4 g/L) and excess (1 g/L) hydrocortisone and only a moderate enhancement of the bioconversion by free cells was observed. This result was explained by a better ultrasound-induced dispersal of microscopic clumps of cells and self-adhering clusters of the steroids. However, a quite significant enhancement effect was obtained in bioconversion systems of soluble substrate by gel-entrapped cells. This enhancement was explained by a phonophoretic effect associated with ultrasound-facilitated diffusion of the substrates - oxygen and hydrocortisone - within the gel beads.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 150
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 1037-1042 
    ISSN: 0006-3592
    Schlagwort(e): biodegradation ; organic solvents ; biooxidation ; bacteria ; competition interactions ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Much more information concerning the biodegradation kinetics of mixtures of common industrial chemicals, such as organic solvents, needs to be gathered before wastewater biotreatment process performance can become a matter of design. Here, the biooxidation of a solvent mixture comprizing methanol, acetone, isopropanol, and methylene chloride is examined. The fact that the enrichment culture obtained comprized only two solvent-utilizing strains, together with only minor percentages of nonsolvent utilizing satellite strains, was contrary to the theory of microbial competition. In addition, the complex relationship between the two solvent-utilizing strains indicates that further work is necessary on the pathways involved in isopropanol and acetone biooxidation and on the effects of operating conditions on the fluxes along such pathways.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 151
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 1066-1075 
    ISSN: 0006-3592
    Schlagwort(e): Resonance energy transfer ; papain ; concanavalin A ; molecular model ; monovalent ligand and receptor ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A stochastic model is described that predicts the degree of singlet/singlet energy transfer in complexes formed between monovalent ligands and monovalent receptors. The modeling approach is intended to serve as an analytical tool for approximating the level of fluorescence quenching that can be expected to occur in fluorescently labeled monovalent ligands and receptors that are bound together in complexes. This approach has utility in areas such as modeling protein/protein interactions and designing fluorescence energy transfer assays.Using the crystallographic data for papain (monovalent ligand ) and concanavalin A (monovalent receptor ) along with a molecular graphics computational package the ligand and receptor were docked together to form a ligand/receptor complex. The intermolecular distances between the lysine resides of the ligand and receptor were then estimated, receptor complex was calculated assuming a value for the characteristic length R0 of the donor/acceptor pair. Results from the stochastic model were used to calculate the level of fluorescence quenching one would expect for a resonance energy transfer competition assay based on the monovalent ligand/pair.Three key assumptions were made during the model development. First, all lysine resides for the ligand and receptor were equally reactive with the dye molecules so the stoichiometry of the donor and acceptor chromophores was governed by a binomial distribution. Second, the dye molecules were located at the α-carbon position for each reactive lysine residue. Finally, in the energy transfer competition assay, it was assumed that equilibrium existed between the ligand, receptor, and competing hapten at all times. Based on these assumptions, results are presented that indicate the maximum energy transfer for the monovalent papain/concanavalin. A complex is strongly dependent on the number of acceptor chromophores and on the value of R0. Results are also presented on the approximate level of fluorescence quenching that may occur in a competition assay based on the papin/pConA complex. Lastly, a strategy is discussed for maximizing the dynamic range and linearity of energy transfer assays by optimizing several key design variables.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 152
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 1108-1116 
    ISSN: 0006-3592
    Schlagwort(e): organic acids ; Aspergillus flavus ; molar yield ; stirred fermentor ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Effects of various nutritional and environmental factors on the accumulation of organic acids (mainly L-malic acid) by the filamentous fungus Aspergillus flavus were studied in a 16-L stirred fermentor. Improvement of the molar yield (moles acid produced per moles glucose consumed) of L-malic acid was obtained mainly by increasing the agitation rate (to 350 rpm) and the Fez+ ion concentration (to 12 mg/L) and by lowering the nitrogen (to 271 mg/L) and phosphate concentrations (to 1.5 mM) in the medium. These changes resulted in molar yields for L-malic acid and total C4 acids (L-malic, succinic, and fumaric acids) of 128 and 155%, respectively. The high molar yields obtained (above 100%) are additional evidence for the operation of part of the reductive branch of the tricarboxylic acid cycle in L-malic acid accumulation by A. flavus. The fermentation conditions developed using the above mentioned factors and 9% CaCO3 in the medium resulted in a high concentration (113 g/L L-malic acid from 120 g/L glucose utilized) and a high overall productivity (0.59 g/L h) of L-malic acid. These changes in acid accumulation coincide with increases in the activities of NAD+-malate dehydrogenase, fumarase, and citrate synthase.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 153
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 30-36 
    ISSN: 0006-3592
    Schlagwort(e): lipase-catalyzed hydrolysis ; 2-naphtyl ester ; biphasic system ; interfacial reaction ; two-film model ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The authors measured the rate of hydrolysis of the homologs of 2-naphtyl ester by using a Lewis cell with constant interfacial area to elucidate the kinetic mechanism of the lipase-catalyzed hydrolysis in biphasic system. On the basis of the two-film model, it was found from the analysis of experimental results that the hydrolysis of these substrates proceeds at the interface between the aqueous and organic phases. The interfacial reaction rate could be correlated by Michaelis-Menten mechanism. The values of the rate constant and the Michaelis constant were almost independent of the kinds of 2-naphtyl ester. The values of the interfacial kinetic parameters for 2-naphtyl ester were much greater than those for the hydrolysis in the aqueous phase.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 154
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 65-74 
    ISSN: 0006-3592
    Schlagwort(e): Succinoglucan ; Agrobacterium radiobacter ; Structured model ; ATP ; cofactors balances ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Wild-type Agrobacterium radiobacter NCIB 9042 has been cultivated in batch cultures on a synthetic medium which was adapted for growth and succinoglucan production. Experiments were carried out in a 4-L stirred-tank aerated reactor. Glucose, biomass, polysaccharide, protein, and inorganic- and organic-nitrogen concentrations were measured, and oxygen consumption and CO2 production rates were obtained by a gas-balance technique. Nitrogen balance shows that inorganic nitrogen is entirely recovered into proteins. The carbon balance is satisfied with in ±5%. Stoichiometric equations for biomass growth and succinoglucan synthesis were established. The biosyntheticpolymer pathways including ATP and cofactor consumption were investigated. From previous studies, a (P/O) value of 1.66 is selected for oxygen sufficient cultures. The actual ATP requirements of 25.4 mmol ATP/g succinoglucan (38.5 mol ATP/mol succinoglucan), determined by a metabolic analysis, is 2.39 times the stoichiometric value. Experimental results were modeled by a system of differential equations. The exponential growth phase was described by a nitrogen-limited Monod equation. Subsequent succinoglucan synthesis followed a slightly modified Luedeking-Piret relation partitioning internal and external polysaccharide. Experimentally determined coefficients are compared with published results for continuous culture of A. radiobacter NCIB 11883.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 155
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 99-103 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Sensors for the simultaneous determinations of sucrose and glucose, lactose and glucose, and starch and glucose were prepared by a combination of the enzyme system shown below and an oxygen electrode: The mechanism for separating the substrates with the proposed sensors is based on the time lag arising from reaction and diffusion. Invertase, β-galactosidase, amyloglucosidase, mutarotase, and glucose oxidase were covalently immobilized on triacetyl cellulose membranes containing 1,8-diamino-4-aminomethyloctane. A glucose oxidase membrane, mutarotase membrane, three sheets of triacetyl cellulose membranes, and invertase, or β-galactosidase or amyloglucosidase membrane were placed in that order on the tip of the oxygen electrode. Calibration curves for sucrose, lactose, and starch were linear up to 40 mM, 60-180 mM, and 10%, respectively. The simultaneous determination of sucrose and glucose, lactose and glucose, and starch and glucose was possible when the amount of glucose coexised was in the range of 2-16% sucrose, 2.8-8.3% lactose, or 0.1-1% starch. The relative errors were ±4% for sucrose and ±3% for lactose in 100 assays. The starch sensor was reused only five times. Each enzyme membrane was fairly stable for more than 10 days.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 156
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 127-134 
    ISSN: 0006-3592
    Schlagwort(e): Bacillus subtillis ; binding free energy ; Adsorption isotherm ; monolayer adsorption process ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The goal of this work was to characterize the adsorption of Bacillus subtills α-amylase onto crystalline starchy materials of the B-type polymorph. Monodisperse spherulitic particles (R ż6; 5.0 μm), essentially resistant to α-amylolysis at 25°C were prepared from short amylose chains (DPn ≈ 15). The α-amylase adsorbed specifically onto the spherulites, and adsorption was found to be a prerequisite step for hydrolysis. Adsorption was inhibited by the presence of maltose and maltotriose in the reaction mixture. Adsorption isotherm of the enzyme on the particles showed a well developed plateau of 1.62 μg/cm2 at 25°C corresponding to a monolayer adsorption process. The binding free energy calculated from the initial slope of the isotherm was ΔG ≈ -20.7 kJ/mol. This is smaller than published values for the binding of α-amylase to soluble amylosic chains (ΔG 〈 -30 kJ/mol).
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 157
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991) 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 158
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 1004-1009 
    ISSN: 0006-3592
    Schlagwort(e): esterification ; immobilized enzymes ; enzymes in organic solvents ; enzyme activity and stability ; continuous enzymatic synthesis ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Various esters were synthesized in nearly anhydrous hexane from alcohols and carboxylic acids using a lipase from Candida cylindracea. The enzyme was immobilized on a nylon support and protein loadings as high as 10 mg/g were obtained. The activity of the immobilized enzyme was maximum in a range of temperatures from 25 to 37°C. Ethylpropionate was formed from ethanol and propionic acid at a rate of 0.017 mol/h g immobilized protein. Different esters were formed at comparable rates and equilibrium conversions could generally be approached in less than 10 h in a batch reaction system. The immobilized lipase catalyst was quite stable and retained about one third of the initial activity after repeated experiments during the course of 72 days. A stirred tank continuous flow reactor was used successfully for the continuous production of esters.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 159
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 1029-1036 
    ISSN: 0006-3592
    Schlagwort(e): immobilization ; protein production ; continuous culture Saccharomyces cerevisiae ; plasmid stability ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The Saccharomyces cerevisiae strain Mc16/p520 has an unstable plasmid, p520, which directs production of a wheat α-amylase. The effects of immobilizing this microorganism on the plasmid stability and the specific productivity of the secreted α-amylase were investigated. Small gelatin beads were used as the support in both fluidized and packed bed configurations, and the yeast cells were attached by covalent cross-linking with glutaraldehyde. These data were then compared to those for nonimmobilized, suspension cells.Plasmid stability was increased for the immobilized cells during continuous culture at dilution rates both above and below washout. Continuous suspension cultures were not stable and rapidly lost the plasmid. Immobilization caused an increase in specific and volumetric productivity during continuous culture, with a packed bed design resulting in the highest specific productivity.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 160
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 1050-1053 
    ISSN: 0006-3592
    Schlagwort(e): hybridomas ; immobilization ; oxygen ; respiration ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Oxygen consumption by hybridoma cells immobilized in 1- and 3.9-mm-diameter calcium alginate beads was measured. The entrapped cells consumed oxygen at about 10 μmol/min per 109 cells, regardless of the bead size and cell loading. In contrast, the same cells in suspension culture respire at specific rates of 3-8 μmol/min per 109 cells (depending on the cell density). The growth rate of the immobilized cells was significantly reduced, while specific antibody production was comparable to that of free cells.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 161
    ISSN: 0006-3592
    Schlagwort(e): homogenization, high-pressure ; cell disruption ; inclusion bodies ; size distribution ; centrifuge, analytical ; Escherichia coli ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The high-pressure homogenization of Escherichia coli, strain JM101, containing inclusion bodies of recombinant porcine somatotropin was investigated. A novel technique employing an analytical disc centrifuge was used to monitor the disruption. This a direct technique which measures cell disintegration rather than soluble protein release. The technique is particularly suited to measurements where the disruption approaches 100%. The disk centrifuge provides a size distribution of the homogenate, and furnishes evidence for the preferential disruption of larger cells. For E. coli containing inclusion bodies, and increase in the cell feed concentration from 145 g/L (wet weight) to 330 g/L resulted is poorer homogenization. Poorer disruption was also obtained by lowering the feed temperature from 20°C to 5°C. Only slight variations in performance were obtained by increasing the feed pH from 7.5 to 9.0 or by storing the feed at 4°C for 24 h prior to disruption. Comparison with uninduced E. coli strain JM101, showed that the disruption obtained is higher for bacteria containing a recombinant inclusion body.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 162
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1247-1252 
    ISSN: 0006-3592
    Schlagwort(e): batch culture ; Bacillus brevis ; esterase ; host-vector system ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The productivity of extracellular enzyme was evaluated in batch culture using a protein hyperexcreting host, Bacillus brevis HPD315 harboring pHSC131, which carried a gene (est) encoding esterase activity from Bacillus stearother mophilus. Optimum temperature and pH for the bacterial growth and the production of extracellular esterase were found to be 35°C and pH 6.5, by using the standard medium (GPY) containing neomycin as a selective pressure, Under the cultivation condition employed, cell growth reached 5 g dry cell weight/L, while the extracellular esterase activity amounted to 4.5 U/mL. Most (79%-92%) of the esterase produced was excreted into the medium. pHSC131 was stably retained in the host cell during cultivation in the presence of neomycin. However, in the absence of neomycin, the plasmid was completely lost from the host after 12-h cultivation accompanied by decreases in both esterase activity and production of total extracellular protein. The copy number of the plasmid was estimated to be approximately 7 throughout the cultivation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the excreted proteins showed the presence of a protein having an apparent molecular weight of 32,000, which equals to the value predicted from the DNA sequence of the est gene.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 163
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 12-16 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The ability of L-sorbose to stimulate cellulase production In shake flask culture of Trichoderma reesei was examined in mineral salts media (initial pH 5.0) containing either 1.0% D-xylose, 1.0% cellulose, and/or 0.1, 0.3, or 0.5% L-sorbose. When sorbose was the only carbon source, growth was limited, little substrate was utilized, pH increased, and cellulase activity was not apparent. The other carbon sources promoted good growth, pH dropped sharply to 2.5-3.0, substrate was utilized rapidly, and cellulase activity was detected. After three weeks of fermentation, twice as much cellulase activity was detected in the medium containing only cellulose as the carbon source, as compared to xylose as the carbon source. Cellulase activity was higher when media contained xylose supplemented with sorbose compared to xylose as the only carbon source. At 0.3 and 0.5% levels of sorbose supplementation of xylose-based media, cellulase activity was similar to that in cellulose-based media.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 164
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 35-46 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Two murine hybridoma cell lines (167.4G5.3 and S3H5/γ2bA2) were adapted to grow in low-serum and serum-free media by a weaning procedure. The changes in cell growth, metabolic, and antibody production rates with adaptation were examined using biochemical and flow cytometric analyses. After adaptation to a particular serum level, the short-term serum response of the cells was experimentally determined. Specific growth rates, glucose and glutamine uptake and lactate and ammonia production rates, and specific antibody production rates were evaluated from the data. For both cell lines, an improvement in cell growth was observed after adaptation, and both higher growth rates and higher cell concentrations were obtained. The specific glucose and glutamine uptake rates and the lactate and ammonia production rates changed insignificantly with adaptation. Conversely, changes in the specific antibody production rate of the two cell lines differed. Cell line 167.4G5.3 showed a loss in antibody productivity at low serum levels, while the S3H5/γ2bA2 kept its original productivity in low-serum-containing media. The intracellular antibody content for S3H5/γ2bA2 cells remained unaltered by adaptation, but a low antibody containing cell population appeared in the 167.4G5.3 culture. The loss of specific antibody productivity in this cell line was due to the appearance of this population.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 165
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 80-92 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Axial and radial oxygen depletion are believed to be critical scale-limiting factors in the design of cell culture hollow fiber bioreactors. A mathematical analysis of oxygen depletion has been performed in order to develop effectiveness factor plots to aid in the scaling of hollow fiber bioreactors with cells immobilized in the shell-side. Considerations of the lumen mass transport resistances and the axial gradients were added to previous analyses of this immobilization geometry. An order of magnitude analysis was used to evaluate the impact of the shell-side convective fluxes on the oxygen transport. A modified Thiele modulus and a lumen and membrane resistance factor have been derived from the model. Use of these terms in the effectiveness factor plots results in a considerable simplification of the presentation and use of the model. Design criteria such as fiber dimensions and spacing, reactor lengths, and recycle flow rates can be selected using these plots. Model predictions of the oxygen limitations were compared to experimental measurements of the axial cell distributions in a severely oxygen limited hollow fiber bioreactor. Despite considerable uncertainty in our parameters and nonidealities in hollow fiber geometry, the cell distribution correlated well with the modeling results.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 166
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 877-882 
    ISSN: 0006-3592
    Schlagwort(e): microtechnique ; microprobe ; biofilm ; dissolved oxygen concentration ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A novel in situ microtechnique allows evaluating parameters of diffusion-controlled reactions in biofilms. A microprobe, 15 μm in diameter, was used to simultaneously measure the dissolved oxygen concentration and the optical density at different depths in a submerged biofilm. Based on the results, the biofilm diffusion coefficient for dissolved oxygen, Df the dissolved oxygen flux through the biofilm surface, J02, and the half velocity coefficient, Ks, have been calculated.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 167
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 907-922 
    ISSN: 0006-3592
    Schlagwort(e): fluorescene monitoring ; inner-filter effect ; biosensor ; tryptophan ; tyrosine ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: An extensive fluorescence database for binary tyrosinetryptophan mixtures utilizing 280 nm excitation was collected. The database spanned three orders of magnitude (10-6M-10-3M) and covered all compositions within this range. A generalized model for describing the multicomponent fluorescence signals as a function of emission wavelength, excitation wavelength, and sample composition was derived. A geometric integral that contained all the geometric factors affecting fluorescence was introduced; thus the model was applicable to various configurations, including the three used in this study: an NADH probe, a backscatter laser-induced fluorescence setup, and a commercial spectroflurometer. A correction factor was proposed that allowed linearization of the fluorescence signals with respect to fluorophore concentrations. The effect of the water Raman on fluorescence spectra was also modeled. The model contains only two wavelength-dependent parameters for each of the components present in a sample, one specifying absorption of the excitation energy and the other specifying the species' fluorescence tendency. These wavelength-dependent parameters were correlated with polynomials. The average prediction error at each wavelength was 10-20%, a major portion of which was attributed to experimental uncertainties.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 168
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 952-955 
    ISSN: 0006-3592
    Schlagwort(e): human albumin ; Protein conjugate ; caionic polymer ; PEG chains ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Human albumin has been attached to 24-hole polystyrene plates via branched poly(ethylene lycol) (PEG) spacer arms. A tetraepoxude of PEG of molecular weight (1.4-1.5) × 104 g/mol was reacted with the protein in solution allowing approximately one-third of the oxirane rings to react. The protein conjugate was then coupled to the long, cationic polymer poly(ethylene imine) (PEI), and the protein-PEG-PEI adduct was subsequently adsorption to unmodified polystyrene. Since the protein is linked to the surface via long, hydrophilic and nonchargedchains, interactions between the biomolecule and the surface is minimized.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 169
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991) 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 170
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 977-985 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A novel method has been developed for the separation of bioproducts from yeast cells. The method uses a combination of physical, chemical, and biological agents such as lytic enzymes, osmotic supports, and spheroplast stabilizers. Using this technique, products (proteins and enzymes) can be released from specific cell locations at different process states; it has thus been celled differential product release (DPR). The wall-associated proteins are released first and the lytic enzyme is removed together with the wall proteins at this stage. Secondly, the cytosol products are released by a mild procedure during which the organelles remained intact. Finally, the organelle proteins are solubilized. In each stage, specific proteins are released while others are kept inside the different cell compartments. This method can be used with relatively high yeast concentrations (up to 145 g dry wt/L) and gives higher product recoveries and much higher selectivity than mechanical disruption.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 171
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 781-787 
    ISSN: 0006-3592
    Schlagwort(e): hybridoma culture ; monoclonal antibody production ; perfusion culture ; continuous culture ; cell cycle ; tangential filtration ; cell separation ; nuclepore membranes ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: In order to elucidate the hybridoma life cycle and the limiting factors in perfusion systems, we performed cultures in a stirred tank bioreactor, coupled to an external tangential flow filtration unit. Cell density and antibody production in perfusion were consistent with previous studies. The average life span of the cells (2.1-2.2 days), antibody, productivity per cell produced (30-38 mg/109 cells) and cell size diameter evolution appeared similar to values observed in batch cultures. These observations highly suggest a similar “grow or die” life cycle. Cell and antibody production, strictly related to the medium perfusion rate, seem to be under the control of the nutrient availability. A hypothesis to explain such a life cycle of hybridoma cells in perfusion systems and a model for viable and dead cell density is proposed.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 172
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 813-820 
    ISSN: 0006-3592
    Schlagwort(e): loading rate ; growth yield ; oxidation rate ; free-cell suspensions ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Kinetic parameters of biological sulfide oxidation are described. The influence of the sulfide loading rate on growth yield and specific oxidation rate were investigated with free-cell suspensions. It is concluded that at least two types of bacteria were present, namely, sulfate producers (type A) that grow at higher loading rates. Type A bacteria have a growth yield of 04 g dry S/mol S, while type B bacteria have a growth yield of 04 g dry S/mol S. Type A has a high affinity for sulfide and is inhibited by sulfide at sulfide concentrations exceeding 10 mg/L. Type B has a low affinity for sulfide and is not inhibited by sulfide, but by oxygen.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 173
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 853-868 
    ISSN: 0006-3592
    Schlagwort(e): A spergillus niger ; continuous hydrolysis ; membrane reactor ; butteroil ; immobilized lipase ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A lipase from A spergillus niger, immobilized by adsorption on a microporous, polypropylene flat-sheet membrane, was used to effect the continous hydrolysis of the glycerides of melted butterfat at 35°C. For the reaction conditions used in this research, a pseudo-zero order rate expression can be used to model the kinetics of the overall hydrolysis of butterfat. Multiresponse nonlinear regression methods were employed to determine the kinetic parameters of a multisubstrate rate expression derived fro ma mechanism based on the general Michaëlis-Menten approach. For the multiresponse data taken at pH 7.0, the dependence of the maximum rate of release of each fatty acid residue of butterfat on its carbon chain length is accurately described by a skewed, bell-shaped (or Γ-type) distribution. Data taken at five different pH values were fit assuming a Dixon-Webb diprotic model for the pH dependence of the reaction rate. The thermal deactivation of the immobilized lipase obeyed first-order kinetics with a half-life of 19.9 days at 35°C. The multisubstrate model is useful for the prediction of the free fatty acid profile of lipolyzed butterfat, whereas the lumped-substrate model provides an estimate of the overall degree of hydrolysis as a function of the reactor space time.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 174
    ISSN: 0006-3592
    Schlagwort(e): Aspergillus awamori ; low protease production ; dinitrosalicylic method ; xylanase ; β-xylosidase ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A growth medium was developed for maximal production in batch culture of extracellular xylanase and β-xylosidase by Aspergillus awamori CMI 142717 and a mutant (AANTG 43) derived from the wild-type strain. The optimum pH for the production of xylanase and β-xylosidase was 4.0. The best temperature of xylanase production was 30°C; 35°C was optimal for β-xylosidase. Protease production was never completely suppressed under any of the conditions tested. However, protease titre was 3.5-fold less than the control in medium in which proteose peptone and yeast extract were omitted: the level of xylanase was not affected (8.6 U mL-1) but β-xylosidase titre was increased 4.7-fold to 1.5 U mL-1. When corn steep liquor was used as the sole nitrogen source, xylanse and β-xylosidase titres were further increased by 1.5- and 1.9-fold, respectively. Of the carbon sources investigated, ball-milled oat straw or oat spelt xylan produced the highest titres of xylanse and β-xylosidase. None of the soluble carbon sources investigated produced the high titres of xylanase or β-xylosidase induced by either oat straw for xylanse and β-xylosidase was 2% and the optimum spore inoculum was between 106 and 107 spores/mL-1 final concentration. The level of xylanse activity obtained in the culture filtrates of the mutant was a remarkable 820 U mL-1 when the reducing sugar released was measured by the dinitrosalicylic acid method. This enzyme titre would appear to be the highest reported so far. The xylanases system contained the correct balance of enzymes to effect extensive hydrolysis of oat spelt xylan. The protease titre was very low.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 175
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 941-947 
    ISSN: 0006-3592
    Schlagwort(e): Streptomyces clavuligerus ; cephalosporin ; rate-limiting enzyme ; kinetic model ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A kinetic model describing the cephalosporin biosynthesis in Streptomyces clavuligerus was developed. Using previously reported kinetic data of biosynthetic enzymes, we examined the kinetics of cephalosporin production. The predicted time profile of the specific production rate during a batch culture parallels that of experimental observation. Sensitivity analysis reveals that δ-(L-α-aminoadipyl)-L-cysteinyl-D-valine (ACV) synthetase is the rate-limiting enzyme. The effect of amplifying ACV synthetase on the specific production rate was analyzed theoretically. Increasing ACV synthetase enhances the production rate initially until ACV synthetase enhances the production rate initially until deacetocycephalosporin C hydroxylase becomes rate-limiting. Such kinetic analysis can provide a rational basis for modifying the biosynthetic machinery of cephalosporin through gene cloning.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 176
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 371-374 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 177
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 386-388 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Gel materials are often used to entrap biological catalysts. Several experimental methods have been proposed to estimate the diffusion coefficient of important chemical species within these materials. An error analysis for the bead method was performed and, contrary to previously reported results, when proper experimental conditions were employed, the error associated with the bead method was similar to that obtained using the other common methods.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 178
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 404-414 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The plasmid stability under the repressed state of cloned gene was studied theoretically as well as experimentally using recombinant E. coli K12ΔH1Δtrp/pPLc23trpA1 as a “host-vector” model system. The important kinetic parameters studied were the plasmid loss rate (θ) describing the rate at which the plasrnid-harboring cells lose plas-mids and the plasmid-free cells are generated per unit time and the difference in growth rates (Δ) between the two genotypes. These parameters were carefully defined, studied, and compared with other key kinetic parameters involved in the recombinant fermentation to further our understanding of metabolism of recombinants. The ratio of the concentration of plasmid-free cells to plasmid-harboring cells (Ω) was introduced, and the mathematical model was derived and used for the determination of the kinetic parameters associated with plasmid instability. These methods developed based on the theoretical considerations were tested experimentally. The results of these methods were compared, and the best method was selected and recommended. The effect of temperature and dilution rate on kinetic parameters θ and Δ were also studied in continuous culture, in order to provide some practical information related to the operation and control of recombinant fermentation processes.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 179
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 445-455 
    ISSN: 0006-3592
    Schlagwort(e): synergism antagonism ; metal uptake ; Chlorella vulgaris ; cadmium ; zinc ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Many microorganisms are capable of sequestering and concentrating heavy metals from their aqueous environment. While much research has beep carried out on the uptake of single species of metal ions, little attention seems to have been given to the study of multimetal ion systems. A mathematical model has previously been developed to describe the uptake of individual metal species by a microorganism. The model proposes two sequential processes: an initial rapid uptake due to cellular surface adsorption and a subsequent slow uptake due to membrane transport of the metal into the cells. This article extends the treatment by considering the uptake of two metal species together, cadmium and zinc, under different experimental conditions. The results are discussed in terms of possible mechanistic interactions.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 180
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991) 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 181
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1110-1113 
    ISSN: 0006-3592
    Schlagwort(e): high-density freezing ; high-density culture ; hybridoma ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Large-scale, high-density freezing of hybridomas was studied to apply frozen cells to start high-density culture. We showed here that hybridomas can be frozen at 1.5 × 108 cells/mL, without decrement in viability and proliferating activity. Blood transporting bags were used for large-scale freezing to store 25 mL of cell suspension with a cell density, 1.5 × 108/mL. The number of cells stored in a bag (3.0 × 109 cells) was enough to start a high-density culture at a 10 times higher cell density (6.0 × 106 cells/mL) than normal inoculation, and the cells proliferated to 107 cells/mL within 2 days. These results indicate that the large-scale freezing method is useful for large-scale culture of mammalian cells.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 182
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1114-1117 
    ISSN: 0006-3592
    Schlagwort(e): L-2-halo acid dehalogenase ; dehalogenation ; in dimethyl sulfoxide ; 2-hydroxy acids ; stereospecific production of substrate specificity ; change in organic solvent ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A Lyophilized preparation of L-2-halo acid dehalogenase was not only stable but also catalytically active in anhydrous dimethyl sulfoxide, toluene, and other organic solvents. 2-Halo acids with long alkyl (C5-C16) or aromatic (phenyl and benzyl) side chains were inert in water but dehalogenated effectively in anhydrous dimethyl sulfoxide by the lyophilized enzyme. Long chain 2-haloalkanoic acids such as 2-bromohexadecanoic acids were better as substrate than short-chain halo acids (e.g., 2-chloropropanoic acid). The dehalogenation proceed with inversion of C2 configuration to produce the corresponding (2R)-2-hydroxy acids in anhydrous dimethyl sulfoxide in the same way as found in water.
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
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  • 183
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1144-1152 
    ISSN: 0006-3592
    Schlagwort(e): stabilization of chymotrypsin ; enzyme-support multipoint attachment ; effect of denaturing agents ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: We have developed a strategy for immobilization-stabilization of α-chymotrypsin by multipoint covalent attachment of the enzyme, through its amino groups, to agarosealdehyde gels. We have studied the role of the main variables that control the intensity of these enzyme-support multi-interaction processes (surface density of aldehyde groups in the activated gel, contact time between the immobilized enzyme and the activated support prior to borohydride reduction of the derivatives, etc.). In this way, we have prepared a number of very different chymotrypsinagarose derivatives. Our best derivatives, with the most intense multipoint attachment, were more stable than one-point attached derivatives and were more than 60,000-fold more stable than soluble enzyme in the absence of autolysis phenomena. In spite of the dramatic stabilization, the catalytic activity of these derivatives is little changed (they only lose 35% of intrinsic activity after this intense enzyme-support multi-interaction process). In addition, we have also demonstrated the very high capacity of 6% aldehyde-agarose gels to immobilize pure chymotrypsin (40 mg enzyme/mL catalyst). Furthermore, we have been able to establish a clear correlation between enzyme-support multipoint covalent attachment, stabilization against very different denaturing agents (heat, urea, organic cosolvents), and insensitivity of those immobilized chymotrypsin molecules to some activating agents.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 184
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1173-1181 
    ISSN: 0006-3592
    Schlagwort(e): Streptococcus cremoris ; continuous three stage fermentation ; ammonium lactate ; whey permeate ; FACWP ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Batch and continuous fermentation studies were performed to optimize the production of ammonium lactate from whey to optimize the production of ammonium lactate from whey permeate. The product known as fermented ammoniated condensed whey permeate (FACWP) is a very promising animal feed. After an initial screening of four strains which produce predominantly L(+)- lactic acid, the desired isomer [D(-)-lactic acid is toxic], Streptococcus cremoris 2487 was chosen for further study. In batch mode, pH between 6.0 and 6.5 and 35°C provided optimum incubation conditions. To stimulate a plug flow reactor, three CSTRs (continuous stirred tank reactors) were connected in tandem. For a 7.5-h retention time, 1.6-fold and 1.3-fold higher productivities were obtained for three-stage than for the single- and two-stage reactors, respectively. Various retentions times were examined (5, 7.5, and 10 h; 5g/L yeast extract). Although maximum lactate productivity occurred at a 5-h residence time (5.38 g/L H. 75% lactose utilization), lactose utilization was more complete at 7.5 h (4.38 g/L h productivity, 91% lactose utilization and a productivity, 91% lactose utilization). Retention time was increased to 15 h to obtain 95.9% lactose utilization and a productivity of 2.42g/L h for 2g/L yeast extract. Based on this lower yeast extract concentration, it was determined that ammonium lactate production and subsequent concentration by 11-fold would yield a product (FACWP) 17% more than soybean meal (crude protein contents are equivalent, 44%) at current market prices.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 185
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1210-1217 
    ISSN: 0006-3592
    Schlagwort(e): Δ1,2-dehydrogenation of high steroid concentrations ; microemulsion system ; enzyme kinetics ; biphasic system ; stability in ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The Δ1,2-dehydrogenation of high concentrations of the steroid -methyl-Reichstein's compound S-21-acetate (16MRSA) in a microemulsion system was studied using heat-dried and thawed Arthrobacter simplex cells as biocatalyst. The microemulsion system consists of an organic phase [75-95% (v/v)] with steroid (1-60 g/Ltot), an aqueous phase [5-25% (v/v)] containing the cells (5-30 g/Ltot), and a neutral surfactant (5-20 g/L organic solvent). Benzene derivatives, which solubilize 16MRSA up to 94 g/L, and phospholipids were used as organic solvents and surfactants, respectively, and menadione was added as an external electron acceptor. Factors affecting the dehydrogenation rate in the microemulsion system were studied. The influences of the 16MRSA and the menadione concentration on the dehydrogenation rate were described by Michaelis-Menten kinetics, apparent V′max and K′m values of 2.06 g/g dry weight h and 18.9 g/L for 16MRSA and 4.97 g/g dry weight h and 1.91 g/L for menadione being obtained. Optimal menadione concentration was dependent on the steroid concentration was dependent on the steroid concentration used. The reaction was strongly inhibited by high product concentrations. Much higher activities were obtained with the thawed cells than with the dried cells, conversions of 98% being reached within 14-16 h. for 16MRSA and cell dry weight concentrations of 40 and 10 g/L, respectively. Activity retention in a batch stirred tank reactor remained constant during the first 16-24 h of operation and then decreased, depending on the stirring rate; 22 to 65% of the initial reaction rate was obtained after 48 h at stirring rates of 650 and 2000 rpm, respectively.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 186
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1223-1232 
    ISSN: 0006-3592
    Schlagwort(e): penicillin fermentation ; carbon dioxide effect ; oxygen transfer ; oxygen diffusion ; rheological behavior ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Fermentations of Penicillium chrysogenum have been made with different CO2 contents in the influent gas streams. The rheological behavior of the culture broth was found to be significantly changed by exposure to high levels of CO2. This is attributed to the wide variation in the morphology of P. chrysogenum, from normal mycelia with long hyphae to roughly spherical pellets when subjected to high levels of CO2. A correlation has been developed relating volumetric O2 transfer coefficients, kLa, with the effective O2 diffusion coefficients, De, and the apparent viscosities, μapp, based on the results obtained in this study. The use of CO2 as a potent means for altering the rheological properties of culture broths and consequently improving the O2 transfer capabilities in penicillin fermentations was clearly demonstrated.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 187
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1239-1246 
    ISSN: 0006-3592
    Schlagwort(e): protein extraction ; α-chymotrypsin ; micelles ; reverse ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: α-chymotrypsin is taken as a model protein to investigate three aspects of the protein extraction by reverse micelles: (1) the comparison between the two forward transfer techniques, i.e., the liquid-liquid and the solid state-liquid transfer; (2)the back-transfer, i.e., the capability of the protein to be recovered from the micellar solution; and (3) the maintainance of the enzyme activity at the end of the extraction cycle. Concerning the forward transfer from the liquid phase, we study first the effect of salt initially present in the aqueous phase on the equilibrium concentration of the extracted species; further, we study the forward protein extraction from the solid state, and the effect of pH, salt, and protein concentration on the transfer efficiency. Concerning the back transfer, we find the somewhat surprising result, that the percentage of protein back-extraction depends on the type and concentration of salt used for the forward transfer. Preliminary data concerning an alternative method for the back-transfer using silica gel to liberate the protein from the micellar environment, are presented. Finally, it is found that the enzyme activity depends again on the type and concentration of salt used for the forward transfer.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 188
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991) 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 189
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 859-868 
    ISSN: 0006-3592
    Schlagwort(e): Coffea arabica ; calcium ; phosphate ; cell growth ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Plant, mammalian, and microbial cells are commonly immobilized in calcium alginate gels for the production of valuable secondary metabolites. However, calcium ions are known to inhibit growth in various types of cells, and calcium is an integral part of such gels. Therefore, an investigation was conducted to evaluate the effect of calcium on the growth and alkaloid production of a model cell-line, Coffea arabica, in suspension culture before, attempting to immobilize such cells in alginate. A kinetic model was then developed from the results to describe cell growth and alkaloid production and the mechanism by which calcium influences these variables. In addition, it was observed that there was a characteristic relationship between the concentration of calcium in the external medium and the concentration of extra cellular and intracellular phosphate. The intracellular phosphate level was, in turn, related to the production of alkaloids. Using these results, a dynamic mathematical model of cell growth and alkaloid production was developed based on the proposed roles of calcium and phosphate. The model showed satisfactory agreement with three sets of experiments at different calcium concentrations. A possible linkage between the calcium and phosphate results is postulated based on the limited solubility of calcium phosphate.
    Zusätzliches Material: 16 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 190
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 889-893 
    ISSN: 0006-3592
    Schlagwort(e): oxygen transfer coefficient ; kLa ; pulsed dynamic method ; mechanically agitated vessels ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: This reports on the determination of the overall oxygen transfer coefficient in a mechanically agitated vessel using a randomly pulsed dynamic method. This method consists in exciting the system by randomly switching the inlet gas stream with air or nitrogen with an identical volumetric flow rate. A pseudo-random binary sequence was used. This procedure is routinely used in process control for the identification of system's transfer function. The pulsed dynamic method gives good reliability (as compared with the traditional gassing-out method) and reproducibility in water. However, further improvement is needed before it can be used to monitor on-line the kLa during a fermentation.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 191
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 922-926 
    ISSN: 0006-3592
    Schlagwort(e): transient response method ; rate constants ; immobilized enzyme ; glucose oxidation ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The transient response method was utilized to evaluate the rate constants of reaction over immobilized enzyme. Glucose oxidation catalyzed by the immobilized glucose oxidase in a fixed-bed reactor was selected as an example. A theoretical model including the effects of axial dispersion, film diffusion, and intraparticle diffusion was established for the reactor. The individual rate constant of each elementary step of this enzymatic reaction was determined through direct fitting of the experimental response data to the model.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 192
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 948-954 
    ISSN: 0006-3592
    Schlagwort(e): cellulase ; cellulose hydrolysis ; steam treatment ; ultrafiltration ; enzyme adsorption ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Lignocelluloses (steamed hardwood and hardwood kraft pulp) were semicontinuously hydrolyzed on a large scale [2-2. 5 kg of substrate vs. 20, 000 IU filter paperase (FPase)] using a 10-L hydrolysis reactor with an ultrafiltration unit for the recovery and reuse of cellulases. The substrate was added to the reactor at appropriate intervals to keep a concentration of approximately 5% (w/v). All of the enzyme was added at the beginning and no further addition was done. The ultrafiltration unit was operated intermittently rather than continuously due to its enough capacity (dilution rate of 2.5 h-1) and making the enzyme durable. The enzyme required to produce one gram of reducing sugar in this reactor was 27.3 FPase IU/g RS for steamed hardwood and 7.4 FPase IU/g RS for hardwood kraft pulp. The sugar composition of hydrolyzate was unaltered virtually from beginning to end of the hydrolysis in spite of the progressive loss of enzyme activities. The analysis of the enzyme composition in the hydrolyzate during hydrolysis revealed that an exo-β-D-glucanase component was adsorbed selectively at the stages of advanced hydrolysis extent.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 193
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 973-980 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Pichia stipitis NRRL Y-7124 has potential application in the fermentation of xylose-rich waste streams, produced by wood hydrolysis. Kinetic models of cell growth, death, and oxygen uptake were investigated in batch and oxygen-limited continuous cultures fed a rich synthetic medium. Variables included rates of dilution (D) and oxygen transfer (K1a) and concentrations of xylose (X), ethanol (E), and dissolved oxygen (Cox). Sustained cell growth required the presence of oxygen. Given excess xylose, specific growth rate (μ) was a Monod function of Cox. Specific oxygen uptake rate was proportional to μ by a yield coefficient relating biomass production to oxygen consumption; but oxygen uptake for maintenance was negligible. Thus steady-state COX depended only on D, while steady-state biomass concentration was controlled by both D and K1a. Given excess oxygen, cells grew subject to Monod limitation by xylose, which became inhibitory above 40 g/L. Ethanol inhibition was consistent with Luong's model, and 64. 3 g/L was the maximum ethanol concentration allowing growth. Actively growing cells died at a rate that was 20% of μ. The dying portion increased with E and X.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 194
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 995-997 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 195
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Application of bioreactors is dominated by industrial production with the consequence that bioreactors also for scientific purposes are mainly used following an empiric pragmatic approach. For the sake of a breakthrough in biotechnology in general, and especially for advanced process development, a more systematic approach is emphasized here. This methodology in bioreactor performance studies is explained and the meaning clarified in a case study of a new type of tubular bioreactor. The central role of so-called “model bioreactors” in bench-scale applications is illustrated as a powerful contribution to the optimal design of bioreactors in technical scale. Pilot plant data in case of a tubular reactor for the production of ethanol with Zymomonas and biopesticides with Bacillus thuringiensis are presented.
    Zusätzliches Material: 20 Ill.
    Materialart: Digitale Medien
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  • 196
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 55-64 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The kinetic behavior of a nonproducing hybridoma clone AFP-27-NP was investigated in continuous culture under glucose-limited conditions. A total of more than 21, 000 h of cultures were operated at dilution rates ranging from 0.01 to 0.06 h-1. The viable cell concentrations, dead cell concentrations, and cell volumes all varied with the dilution rate. A steady-state model was developed based on the biomass concentration and the glucose concentration. The specific growth rate as a function of glucose concentration is described by a model similar to the Monod model with a threshold glucose concentration and a minimum specific growth rate incorporated; the model is meaningful only at glucose concentrations and specific growth rates above these levels. A death rate is included in the model which is described by an inverted Monod-type function of glucose concentration. The yield coefficient based on glucose is constant in the lower range of specific growth rates and changes to a new constant value in the upper region of specific growth rates. No maintenance term for glucose consumption was needed; in the plot of specific glucose consumption rate vs. specific growth rate, the line intercepted the specific growth rate axis at a value close to the minimum growth rate. The values for the model parameters were determined from regression analysis of the steady-state data. The model predictions and experimental results fit very well.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 197
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 93-96 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Recent interest in the industrial manufacture of ethanol and other organic chemicals from biomass has led to the utilization of surplus grain and cane juice as a fermentation feedstock. Since those starting materials are also foods, they are expensive. As an alternative, cellulosic substances - the most abundant renewable resources on earth1 - have long been considered for conversion to readily utilizable hydrolyzates.2, 3For the production of ethanol from cellulose, we have proposed the simultaneous saccharification and fermentation (SSF) process.4 In SSF, enzymatic cellulose hydrolysis and glucose fermentation to ethanol by yeast proceed simultaneously within one vessel. The process advantages - reduced reactor volume and faster saccharification rates - have been confirmed by many researchers.5-8 During SSF, the faster saccharification rates result because the glucose product is immediately removed, considerably diminishing its inhibitory effect on the cellulase system.9To effectively apply the SSF method to produce substances fermented from glucose, several conditions should be satisfied. One is coincident enzymatic hydrolysis and fermentation conditions, such as pH and temperature. The other is that cellulase inhibition by the final product is less than that by glucose and/or cellobiose. One of us has reported that acetic acid, citric acid, itaconic acid, α-ketoglutaric acid, lactic acid, and succinic acid scarcely inhibit cellulase.10 This suggests that if the microorganisms which produce these organic acids were compatible with cellulase reaction conditions, the organic acids could be produced efficiently from cellulosic substrates by SSF.In this article, the successful application of SSF to lactic acid production from cellulose is reported. Though there have been several reports of direct cellulose conversion to organic acids by anaerobes such as Clostridium, only trace amounts of lactic acid were detected in the fermentation medium among the low-molecular-weight fatty acid components.11-13 Lactic acid is one of the most important organic acids and has a wide range of food-related and industrial applications.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 198
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 133-140 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Substrate transfer rates from organic to aqueous phases were measured in the presence and absence of biocatalyst in the reaction medium, using modified Lewis cells. These measurements, in combination with intrinsic aqueous phase biocatalytic reaction kinetics, were used to confirm that benzyl acetate hydrolysis by pig liver esterase and toluene oxidation by a strain of Pseudomonas putida occur uniformly throughout the bulk of the aqueous phase. Such data may be used to provide a basis for two-liquid-phase biocatalytic reactor design.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 199
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 160-176 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Enzyme-potentiometric sensors in which the chemical conversion of the analyte leads to the formation of an acid and/or a base can often display complex response characteristics. In these sensors, the, electrochemically monitored species is usually the H+ ion (pH-based sensors). However, in some cases the conjugate-ion of the H+ (or OH-) ion of the acid (or base) produced-can also be monitored - a specific example being the urease-NH4+ sensor. The response of both types of sensors is strongly affected by: (1) the degree of dissociation of the products and their transport properties in the enzymic film, (2) the amounts of pH-buffers present in the test solution, (3) the test solution's pH, and (4) the diffusion coefficients of the various species. In this article, a previously developed theoretical model for pH-based sensors - in which the differences in diffusivities of the various species were ignored - is generalized to accommodate for such differences, and extended to the latter of the above two types of sensors. It is shown that when the sensor operates under analyte diffusion-controlled conditions, the response of either type of sensor can be predicted by a simple algebraic equation which is independent of the actual kinetics of the enzymic reaction.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 200
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991) 
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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