THE ROLE OF CALCIUM IN TAKA-AMYLASE A

II. THE EXCHANGE REACTION OF CALCIUM

Abstract

1. The firmly bound calcium atom in TAA is able to exchange in solution with free exogenous calcium ions but not with strontium ions.
2. During repeated crystallization procedure the calcium atom ex-changes not only with calcium but also with strontium and magnesium ions. The exchange rate is greatest with calcium and smallest with magnesium.
3. The preparations of TAA produced by A. orytae grown in the media containing no added calcium was found to possess a considerable amount of non-dialysable calcium which might have been derived from impurities.
4. The TAA protein has a strong affinity to calcium, although the bound calcium can be replaced by strontium without loss of the enzymatic activity.
5. During the acid inactivation of TAA and its reactivation by neutralization, the enzymatic activity and the amount of non-exchangeable calcium show a good parallelism.
6. A similar relationship was observed between the enzymatic activity and the change in levo-rotatory power or dispersion constant which may be regarded as a measure of denaturation.
7. The possible role of the essential calcium atom in the maintenance of enzymatic activity of TAA was discussed.
The author wishes to express his gratitude to Prof. S. Akabori for his kind guidance, and to Sankyo Co., Ltd. for their kind supply of “Takadiastase Sankyo”. The author also wishes to thank Otozai Laboratory, Facultfy of Science, Osaka University, for the determination of metals.