A stopped-flow study of the reaction of reduced cytochrome oxidase with oxygen

Abstract

The reaction of a reduced cytochrome oxidase system consisting of beef heart cytochrome oxidase, cytochrome c, and ascorbate with molecular oxygen was kinetically and thermodynamically investigated using a stopped-flow, rapid wavelength-scanning technique. Processes for oxidation of ferrocytochrome a, bound ferrocytochrome c, and free ferrocytochrome c have been identified, and their rate constants have been determined. Values of the activation energy for these reactions indicate that the oxidation of bound ferrocytochrome c is a simple chemical electron-transfer process and that oxidations of ferrocytochrome a and free ferrocytochrome c are complex processes involving changes in protein conformation.