β-アミラーゼのアスコルビン酸に依る阻害に関する研究 : (第3報)酸素圧の影響及び銅イオン存在下の自酸化の過程のアスコルビン酸に依る阻害

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(1) The effect of low oxygen tension on the inhibition of sweet potato β-amylase caused by ascorbic acid plus Cu++ and the inhibition by the same inhibitor in its different stage of autoxidation were studied. (2) Under low oxygen tension, the inhibition by Cu+ survived longer than under aerobic condition and the inhibition of the irreversible type was less serious. (Fig. 1 and Table 1). (3) The intersection of curves, which showed the course of inhibition, as it was illustrated in Figures 5 to 7 in Part 1 of this series, was the effect of condition when the oxygen tension was rate-determining for the autoxidation of ascorbic acid. (4) Under the present experimental condition (pH 5.6 and 2_??_3°), the inhibition by Cu+ survived for several hours even after the complete disappearance of titratable ascorbic acid. (Curve 4 in Fig. 2 and Curve 2 in Fig. 3) (5) The probable cause of the inhibition of the irreversible type was an oxidation of -SH group of enzyme. From the data presented in Figures 2 and 3, it might be concluded that another mechanism of oxidation must be present in addition to the oxidation by the autoxidation product of ascorbic acid (probably by H2O2).
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