Abstract
1. 1. The turnover number and apparent K m 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. 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 K m for cytochrome c. 3. 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 (p K a 8.0, 6.5 and 4.8) can take up a proton.
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