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  • Biochemistry and Biotechnology  (27)
  • Life and Medical Sciences  (4)
  • muon-catalyzed fusion  (3)
  • Amorbia cuneana  (2)
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  • 11
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 28 (1986), S. 996-1006 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Widely applied selection strategies for plasmid-containing cells in unstable recombinant populations are based upon synthesis in those cells of an essential, selection gene product. Regular partitioning of this gene product combined with asymmetric plasmid segregation produces plasmid-free cells which retain for some time the ability to grow in selective medium. This theory is elaborated here in terms of a segregated model for an unstable recombinant population which predicts population growth characteristics and composition based upon experimental data for stable strain growth kinetics, plasmid content, and selection gene product stability. Analytical solutions from this model are compared with an unsegregated phenomenological model to evaluate the effective specific growth rate of plasmid-free cells in selective medium. Model predictions have been validated using experimental growth kinetics and flow cytometry data for Saccharomyces cerevisiae D603 populations containing one of the plasmids YCpG1ARS1, YCpG1ΔR8, YCpG1ΔR88, YCpG1ΔH103, YCpG1ΔH200, pLGARS1, and pLGSD5. The recombinant strains investigated encompass a broad range of plasmid content (from one to 18 plasmids per cell) and probability α of plasmid loss at division (0.05 ≤ α ≤ 0.42). Experimental data for all strains considered is inconsistent with the hypothesis that plasmid-free cells are unable to grow in selective medium. For a given value of a, the fraction of plasmid-containing cells in the population decreases with increasing plasmid content and increases for less stable selection gene products. This conceptual framework and mathematical model will aid in strain development for greater effective stability.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 31 (1988), S. 304-310 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A segregated model of multicopy plasmid propagation has been formulated which incorporates plasmid replication and partition functions, as well as the effect of plasmid presence on host growth rate. Growth of plasmid-free cells in selective medium is explicitly analyzed. The model parameters can be determined from experimentally measurable quantities. Propagation of a recombinant multicopy plasmid in the yeast Saccharomyces cerevisiae is analyzed using this model.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 13
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 32 (1988), S. 725-730 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 14
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 16 (1974), S. 1345-1357 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Many enzyme-catalyzed reactions involve the liberation or consumption of hydrogen ions. In this paper a mathematical model is employed to investigate how such reactions behave when the enzyme is immobilized. Shifted pH optima, disappearance of an optimum pH, insensitivity to bulk pH, and very large effectiveness factors are some of the phenomena which appear as a result of pH coupling between the reaction and the enzyme's activity. Several of the qualitative features revealed by the model are consistent with earlier experimental observations. In addition, preliminary guidelines for optimal choice of enzyme support are suggested.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 15
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 20 (1978), S. 1817-1831 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Immobilization of an enzyme within an insoluble material permeable to substrate can change the apparent behavior of the enzyme. In particular, external mass transfer and intraparticle diffusion effects can significantly influence the dependence of observed reaction rate on operating parameters such as temperature and pH. This analysis shows that, under very general conditions, the influence of diffusion alone is to diminish the sensitivity of the observed rate to any parameter that is uniform throughout the catalyst particle. However, the optimal value of the parameter is not changed because of intrapellet diffusional effects.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 16
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 22 (1980), S. 457-462 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 17
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 25 (1983), S. 2485-2490 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 18
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 34 (1989), S. 902-908 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Experiments were performed to evaluate, qualitatively and quantitatively, the adaptation of Escherichia coli to plasmid maintenance and cloned gene expression. Experimental findings indicate that the metabolic response to low plasmid levels is an increase of the biosynthetic capacity of both transcription and translation. At high copy number levels the gene-specific transcription rate continues to increase but the stability of plasmid-derived mRNA drops sharply. Protein levels are maintained, but translation efficiency decreases. These results indicate that cellular biosynthetic capacity may not be limiting productivity in recombinant systems. If macromolecular stability is the bottleneck, then current efforts to increase gene expression that focus on enhancing synthesis rates will be ineffective.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 19
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1318-1324 
    ISSN: 0006-3592
    Keywords: glucose metabolism ; pet operon ; E. coli ; fermentation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The glucose metabolism of an Escherichia coli strain bearing mutations abolishing both acetyl phosphotransferase (PTA) and acetate kinase (ACK) activities was studied under aerobic and anaerobic conditions. These studies were conducted in a complex medium with the mutant carrying no plasmid, the mutant carrying the common cloning vector pUC19, and the mutant carrying a plasmid bearing the “pet” operon that encodes Zymomonas mobilis pyruvate decarboxylase and alcohol dehydrogenase activities. The mutant carrying no plasmid showed lower specific growth and glucose uptake rates relative to the parent wild-type strain (K-12), Lactic acid was produced at higher levels than the wild type, and considerable amounts of pyruvic acid were secreted as an unusual byproduct. Analysis of other fermentation products showed low but significant amounts of acetic acid, no accumulation of formic acid, and lower secretion of succinate and ethanol. The maintenance of the plasmid pUC19 in the mutant negatively affected metabolism. Expression of the pet operon overcame the metabolic stress caused by the plasmid, enhancing growth and glucose uptake rates to the values observed in the plasmidfree mutant. Also, expression of the pet operon allowed consumption of pyruvate accumulated during the first hours of fermentation.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 20
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 736-745 
    ISSN: 0006-3592
    Keywords: computer image analysis ; electrophoresis patterns ; DNA manipulations ; recombinant Escherichia coli ; metabolic analysis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Relative levels of many individual proteins in Escherichia coli HB101 strains with 0, 37, 56, and 240 plasmids per chromosome were determined by computer image analysis of two-dimensional gel electrophoresis patterns. The plasmids investigated had very similar sequences except for small domains encoding the represser of plasmid replication. At the intermediate plasmid copy number of 56, levels of several of the TCA cycle enzymes (oxoglutarate dehydrogenase complex, succinate thiokinase, and succinate dehydrogenase) as well as in aspartate transcarbamoylase increased. At a plasmid copy number of 240, higher amounts of PEP carboxylase as well as several of the heat shock proteins were observed. Furthermore, at high plasmid levels, significant decreases occurred in growth rate, pyruvate kinase I, pyruvate dehydrogenase complex, unadenylated glutamine synthetase, aspartate transcarbamoylase as well as in several of the proteins involved in translation. Decreases in ribosome content as well as in the free 30S and 50S ribosomal subunit pool fractions were also observed in separate analyses. These results indicate that recombinant DNA manipulations can cause major alterations in numerous host cell properties which could significantly influence cloned protein production or metabolic engineering endeavors.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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