The reduction of cytochrome c oxidase by carbon monoxide.

The rate of formation of the mixed-valence state of cytochrome c oxidase on incubation with carbon monoxide is strongly dependent on pH, supporting the concept that CO itself is the reducing agent. The reaction is biphasic due to the presence of two different enzyme forms in the resting oxidase. The kinetics of the reaction with the major enzyme form suggests an initial rapid binding of CO in a heme pocket of the oxidized enzyme and a subsequent slow intramolecular electron transfer to the cytochrome alpha 3-CuB site. Cytochrome alpha and CuA are not reduced even on prolonged incubation.