The kinetics of electron entry in cytochrome c oxidase.

The kinetics of electron entry in beef heart cytochrome c oxidase have been studied by stopped-flow spectroscopy following chemical modification of the CuA site with mercurials. In this derivative CuA is no longer reducible by cytochrome c while cytochrome alpha may accept electrons from the latter with rates comparable to the native enzyme. The results indicate that CuA is not the exclusive electron entry site in cytochrome c oxidase.