Influence of Molecular Structures of Substrates and Analogues on Taka-amylase A Catalyzed Hydrolyses:I. Effect of Chain Length of Linear Substrates

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  • NITTA Yasunori
    The Laboratory of Biophysical Chemistry, College of Agriculture, University of Osaka Prefecture
  • MIZUSHIMA Minoru
    The Laboratory of Biophysical Chemistry, College of Agriculture, University of Osaka Prefecture
  • HIROMI Keitaro
    The Laboratory of Biophysical Chemistry, College of Agriculture, University of Osaka Prefecture
  • ONO Sôzaburo
    The Laboratory of Biophysical Chemistry, College of Agriculture, University of Osaka Prefecture

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Description

1) Hydrolyses of linear maltodextrins (DP 2--DPn 117) catalyzed by crystalline Taka-amylase A [EC 3. 2. 1. 1] were studied at pH 5.3 and 25°C to determine the rate parameter for each substrate.<br> 2) Michaelis constant, Km (in moler basis), decreased with increasing chain length (n) of glucose unit. Turnover number, V/(E)0, increased with chain length up to n=7 and became practically constant for n more than 7, which suggests that the specificity region of Taka-amylase A spans about 7 glucose units.<br> 3) The dependence of Km and V/(E)0 on chain length of substrate was interpreted in terms of the probability of formation of productive and nonproductive ES-complexes. Based on the assumption that the breakdown rate constant in productive ES-complex, kint, is constant irrespective of chain length of substrate and binding mode, magnitudes of subsite affinities (in free energy units) in the active site were evaluated from the values of V/Km (E)0 for various substrates. Results suggested the presence of a distortion in the productive ES complex.

Journal

  • J Biochem (Tokyo)

    J Biochem (Tokyo) 69 (3), 567-576, 1971

    The Japanese Biochemical Society

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