Studies on Cytochrome a

XIII. Interpretation of the Anomalous Spectral Behaviors of Cytochrome a

Abstract

1. By titration of reduced cytochrome a with oxygen the absorption curve of a true oxygenated form of cytochrome a could be obtained.
2. The effects of native and guanidinated cytochrome c's and ferricyanide on oxygenated cytochrome a were compared with that of acetylated and succinylated cytochrome c's and it was confirmed that one of the dual functions of cytochrome c in the oxidase re-action is that it catalyzes the conversion of the oxygenated to the oxidized form.
3. The differences in the absorbancy changes of cytochrome a at 605 mμ and 444 mμ on addition of ascorbate to the preparation were interpreted in terms of a single compo-nent in the cytochrome oxidase, cytochrome a, based on its cyclic change in its functional state. Kinetic results showed that ascorbate was effective only in reducing cytochrome a in contrast to the effect of cytochrome c, which transfers electron to cytochrome a nda also catalyzes the oxidation of the oxygenated form of cytochrome a.
4. Interpretations of the spectral behaviors of an oxidase system composed of cytochromes a and c in the aerobic steady state were con-sistent with our view on the mechanism of the oxidase reaction.