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5報)温度, pH の影響及びmercaptide形成金属に依る阻害の比較

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1) Effect of temperature and pH on the inhibition of sweet potato β-amylase by -ascorbic acid plus Cu++ has been studied. Moreover, these properties of this inhibition have been compared with those of inhibition caused by other mercaptide-forming heavy metals viz. Ag+. HgCl2 and PCMB. 2) As it was reported previously, this inhibition contains two reactions in series, inhibition by cuprous mercaptide formation (I) and subsequent oxidation of mercaptide by atmospheric O2 (II). From the data presented in Fig. 1, it is presumed that reaction (I) occurs instantaneously, and has no temperature coefficient, while reaction (II) is a slow process and requires activation energy. 3) As pH becomes lower, the extent of reaction (I) decreases presumably as the result of lower affinity of Cu+ to -SH groups of enzyme in such a condition. Consequently reaction (II) proceeds at a slower rate. (Fig. 2_??_Fig. 5) 4) Above-mentioned features of this inhibition including reactivation by cysteine, which was reported previously, are quite the same as those in the case of inhibition by Ag+ and differ in all respects from those by HgCl2 and PCMB. These results are summarised in Table 1.
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