pH值和离子强度对分离的细胞色素C氧化酶稳态活性的影响。

The effect of pH and ionic strength on the steady-state activity of isolated cytochrome C oxidase.

Wilms J, van Rijn J L, Van Gelder B F

Biochim Biophys Acta. 1980 Nov 5;593(1):17-23. doi: 10.1016/0005-2728(80)90004-3.

Abstract

The turnover number and apparent Km of isolated beef-heart cytochrome c oxidase were found to increase continuously when the pH was lowered from 8.6 to 4.6 (turnover number 32-630 s-1). In this pH range neither irreversible denaturation of the enzyme nor an optimum for the turnover number was observed. 2. The turnover number of cytochrome c oxidase was found to be independent of ionic strength. It was concluded that the dependence of the activity of cytochrome c oxidase on ionic strength is caused by a change in the value of Km for cytochrome c. 3. The pH dependence of the turnover number of cytochrome c oxidase can be described by a simple model in which at least three sites on the complex of cytochrome c oxidase with cytochrome c (pKa 8.0, 6.5 and 4.8) can take up a proton.

摘要

当pH值从8.6降至4.6时，发现分离出的牛心细胞色素c氧化酶的转换数和表观Km值持续增加（转换数为32 - 630 s⁻¹）。在此pH范围内，未观察到酶的不可逆变性，也未观察到转换数的最佳值。2. 发现细胞色素c氧化酶的转换数与离子强度无关。得出结论，细胞色素c氧化酶活性对离子强度的依赖性是由细胞色素c的Km值变化引起的。3. 细胞色素c氧化酶转换数的pH依赖性可用一个简单模型来描述，在该模型中，细胞色素c氧化酶与细胞色素c的复合物上至少有三个位点（pKa 8.0、6.5和4.8）可以接受一个质子。