Introducing site-directed mutations in surface-exposed residues of subunit II of the heme aa3 cytochrome c oxidase of Paracoccus denitrificans, we analyze the kinetic parameters of electron transfer from reduced horse heart cytochrome c. Specifically we address the following issues: (a) which residues on oxidase contribute to the docking site for cytochrome c, (b) is an aromatic side chain required for electron entry from cytochrome c, and (c) what is the molecular basis for the previously observed biphasic reaction kinetics
