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  • 1975-1979  (2)
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  • 1
    ISSN: 1572-9699
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Properties of β-glucan synthetase from S. cerevisiae were studied. The enzyme exhibited optimal activity at pH 6.7 and 24 C. Km for UDP-glucose was 0.12mm. Addition of Mg++ or Mn++ stimulated its activity by 60% and 21% respectively. High concentrations of EDTA and hydroxyquinoline were inhibitory. Glucan synthetase was fully active in cell-free extracts. Small concentrations of trypsin or subtilopeptidase A from Bacillus subtilis, caused only a slight increase in glucosyl transferase activity, but larger concentrations destroyed β-glucan synthetase. Acid proteases were neither stimulatory nordestructive. Thus it seemsunlikelythat β-glucan synthetase exists in a zymogen form. Glucan synthetase was unstable. It was inactivated more rapidly at 28 C than at 0 C. The presence of substrate, β-glucan or the protease inhibitors PMSF, Antipain or Pepstatin A did not protect β-glucan synthetase from inactivation. Glucan synthetase was not stimulated by addition of cellobiose or β-glucans. The synthesis of β-glucans was competitively inhibited by UDP (Ki=0.45mm). Glucono-δ-lactone, a known inhibitor of β-glucosidases was a strong non-competitive inhibitor of β-glucan synthetase.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1572-9699
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Cell-free extracts from Aspergillus flavus catalyzed the synthesis of chitin from UDP-GlcNAc. Most of the activity was associated with membrane-rich fractions whereas no activity was detected in the cell walls. Chitin synthetase was activated by fungal acid proteases; animal and plant proteases destroyed it. Upon incubation at 0 C and 28 C chitin synthetase was inactivated, probably by the action of proteases present in the particulate preparations. Maximal activity was obtained at pH 6.6–7.1 and 15 C. Arrhenius plot showed a biphasic curve with the transition at 7 C. E values were 3300 Kcal/mole above this temperature and 15500 Kcal/mole below it. The enzyme was activated by GlcNAc and required a divalent metal, the most active being Mg++. By plotting v vs UDP-GlcNAc concentration a sigmoidal curve was obtained. Km calculated at high substrate concentrations was 20mm. Chitin synthetase was competitively inhibited by polyoxin D (Ki 6.5 μm) and UDP (Ki 1.35mm), the latter giving complex kinetics.
    Type of Medium: Electronic Resource
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