THE INFLUENCE OF IONIC STRENGTH AND POLYCATIONS ON THE OXIDATION OF FERROCYTOCHROME C BY CYTOCHROME C OXIDASE.

Abstract

1. The rate of oxidation of soluble ferrocytochrome c by particulate or purified cytochrome c oxidase (cytochrome c: O2 oxidoreductase, EC 1.9.3.1) is very sensitive to changes in the ionic strength of the reaction mixture. When measured in phosphate buffers of constant I, the reaction shows no optimum in the pH range 5.8 to 7.7. 2. The addition of AlCl3 or SnCl4 to the reaction mixture used by Wainio et al. decreases the pH to values below 4. Cytochrome c shows autoxidizability at this acidity. 3. Partially acetylated cytochrome c shows absorption spectra identical with those of native cyctochrome c, both at room temperature and at the temperature of liquid nitrogen. The acetylated cytochrome c can be readily reduced with hydrogen in the presence of palladium and is not autoxidizable. The acetylated ferrocytochrome c is not oxidized by cytochrome c oxidase, but the acetylated pigment is just as effective as native cytochrome c in decreasing the rate constant for the oxidase reaction. 4. Poly-l-lysine is a potent inhibitor of the cytochrome c oxidase reaction. However, a number of basic amino acids and dipeptides are not inhibitory in greater concentrations (either on a molar basis or on the basis of free amino groups). 5. Wheat germ cytochrome c shows identical properties to mammalian cytochrome c in the cytochrome c oxidase reaction. 6. The data give indications of the requirements for a charged site plus an ancillary group in the reaction of cytochrome c oxidase with soluble cytochrome c.