Studies on the Amphoteric Properties of Taka-amylase A:II. Unmasking of Acid Binding Sites

  • TAKAGI TOSHIO
    the Department of Biology, Faculty of Science and the Division of Physical Chemistry, Institute for Protein Research, Osaka University
  • ISEMURA TOSHIZO
    the Department of Biology, Faculty of Science and the Division of Physical Chemistry, Institute for Protein Research, Osaka University

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Description

1. The ionization behavior of Taka-amy-lase A(TAA) in the acid pH region was studied by pH titration. It was found that more than 20 of the 40 carboxyl groups in a TAA molecule are in a masked state as carboxylate ions and combine with hydrogen ions irreversibly below pH 4.3.<br> 2. From measurement of the optical rotation, it was found that the acid-denaturation of TAA occurs simultaneously with the unmasking of the carboxylate groups.<br> 3. These results, together with the previous observations on the abnormal ionization of phenolic hydroxyl groups in TAA, suggest that carboxylate-phenolic hydroxyl hydrogen bonds play a part in maintaining the stable structure of TAA.<br> The authors wish to thank Sankyo Co., Ltd. for a supply of "Takadiastase Sankyo". The authors are also grateful to the Ministry of Education for a grant covering part of the expenses.

Journal

  • J Biochem (Tokyo)

    J Biochem (Tokyo) 49 (1), 43-48, 1961

    The Japanese Biochemical Society

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