Reversible Inactivation of Cytochrome Oxidase by Disulfide Bond Reagents.

Recent studies on the chemical nature of cytochrome oxidase (cytochrome c :02 oxidoreductase, EC 1.9.3.1) have been concerned largely with the structure of its iron-porphyrin prosthetic group (cj. (l)), the importance of copper as an integral component of the enzyme (e.g. (2-5)), and the possible role of a lipid factor (e.g. (6-8)). By contrast, little work has been done on the nature of the functional groups of the protein moiety which are essential for enzyme activity. We have recently begun to study this problem by examining the effect on cytochrome oxidase of reagents known to react selectively with certain functional groups; this approach has been widely used for determining the nature of the groups essential for the activity of a number of enzymes (e.g. (Q)), including cytochrome c (10-13). By this method, previous workers have obtained evidence that cytochrome oxidase does not contain essential sulfhydryl groups (9, 14). On the other hand, the results described in this report suggest that cytochrome oxidase may contain one or more disulfide groups whose integrity is essential for enzyme activity; all reagents tested which react with disulfide bonds were found to inactivate cytochrome oxidase, and the activity was restored by later treatment with oxidized glutathione or cyatine. A preliminary note describing portions of this work has been published (15).