Studies on cytochrome oxidase. IV. The cytochrome oxidase activity.

where the activity is determined by measuring the rate of oxidation of reduced cytochrome c. Smith (6, 7), Conrad (8, 9), Wainio (10-13) et ~2. have extensively investigated the effect of various factors on the cytochrome oxidase activity measured by System 2 with soluble and insoluble preparations of cytochrome oxidase, whereas among those (14-30) who have employed System 1, Slater (5), using an insoluble heart muscle preparation, seems to have studied the experimental conditions for the cytochrome oxidase assay in the most detail. There has been some disagreement between the results obtained by the two systems. For example, with System 2 the optimal pH for the cytochrome oxidase activity has been found to be in the acidic region (3, 10, 11, 30), whereas with System 1 it has been reported to be in the basic region (22, 24). The present paper describes a study of the effect of various factors, especially the reactant concentrations and pH, on the