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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Applied microbiology and biotechnology 20 (1984), S. 233-237 
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Whole cells of Saccharomyces cerevisiae were entrapped in polymers of 2-hydroxyethylmetha-crylate and sucrose hydrolysis catalysed by its invertase was investigated. Analysis of the experimental results confirmed that diffusional resistance to mass transfer of reactant and product was not induced by immobilization. For the yeast cells in the hydrogel, invertase activity obeyed a Michaelis-Menten kinetic and the value of Km (40 mM) was the same as that for yeast cells in bulk phase. The recovery of biocatalyst activity ranged between 17% and 23%, depending on immobilization temperature; the optimum pH range was found to be slightly wider. Storage stability at refrigerator temperature was quite satisfactory; invertase half-life was 267 days. Operational stability of immobilized cells at 45°C (half-life 110 days) was almost twice that of free cells. Finally, cell distribution in the polymer, observed with a scanning electron microscope, was found to be uniform.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Recently enzyme immobilization techniques have been proposed that are mainly founded on the formation of an enzyme-gel layer onto the active surface of an ultrafiltration membrane within an unstirred ultrafiltration cell. If the membrane molecular-weight cutoff is less than the enzyme molecular weight and hence such as to completely prevent enzyme permeation (once the enzyme solution has been charged into the test cell and pressure applied to the system), a time progressive increase in enzyme concentration takes place at the upstream membrane surface that can eventually lead to gelation and hence to enzyme immobilization. However, depending on the total enzyme amount fed, the maximum enzyme concentration achieved in the unsteady state could be less than the gelation level. In this situation, no immobilization occurs and the enzyme still remains in the soluble form although it is practically confined within a limited region immediately upstream the membrane and at fairly high concentrations. In this paper, the experimental conditions that allow gelling to occur are discussed together with a theoretical analysis of the soluble enzyme membrane reactor which is obtained when no gelling takes place. Such a system could be usefully employed in performing kinetic analyses at high enzyme concentration levels that are still in the soluble form.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-6776
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Linear synthetic polymers markedly increase enzyme thermal stability. The rate of deactivation of acid phosphatase in the presence of polyvinylalcohol and polyvinylpyrrolidone was measured during experiments performed in an ultrafiltration membrane reactor. Protein thermal deactivation obeys an exponential law with a rate constant largely reduced as compared with the corresponding value for the unprotected enzyme. The value of the activation energy of the enzyme denaturation in the presence of each polymer is of the same order of magnitude. Finally, their presence does not interfere with enzyme kinetics since km and Vmax remain unchanged.
    Type of Medium: Electronic Resource
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