抄録
(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).
