在碱性pH条件下Na⁺,K⁺-ATP酶的ADP和氯化钾不敏感磷酸酶中间体的存在
Existence of ADP- and KCl-insensitive phosphoenzyme intermediate of Na+,K(+)-ATPase at alkaline Ph.
作者信息
Siagian R R, Hara Y, Nakao M
机构信息
Department of Biochemistry, Tokyo Medical and Dental University School of Medicine, Japan.
出版信息
Biochem Int. 1990 Oct;22(1):67-74.
The Na(+)-ATPase activity of Na+,K(+)-ATPase in the absence of K+ was least dependent on the sodium concentration when the pH was 9.5. Around 40% of the phosphoenzyme formed from ATP in the presence of 0.5 mM MgCl2 at alkaline pH was insensitive to both KCl and ADP. High-Na+ chase reversed this insensitivity, i.e., the phosphoenzyme became sensitive to KCl or ADP. On the other hand, phosphorylation at 0.1 mM MgCl2 instead of 0.5 mM showed at least 95% sensitivity to KCl. These observations suggest that ADP- and KCl-insensitive phosphoenzyme was formed when excess Mg++ was present during phosphorylation at alkaline pH. This phosphoenzyme might be an intermediate in the process of ATP hydrolysis.
在pH为9.5时，无钾情况下Na⁺,K⁺-ATP酶的Na⁺-ATP酶活性对钠浓度的依赖性最小。在碱性pH值下，0.5 mM MgCl₂存在时由ATP形成的磷酸酶中约40%对KCl和ADP均不敏感。高钠追踪可逆转这种不敏感性，即磷酸酶对KCl或ADP变得敏感。另一方面，在0.1 mM MgCl₂而非0.5 mM下进行磷酸化时，对KCl的敏感性至少为95%。这些观察结果表明，在碱性pH值磷酸化过程中，当存在过量Mg²⁺时会形成对ADP和KCl不敏感的磷酸酶。这种磷酸酶可能是ATP水解过程中的一个中间体。
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