On the role of subunit III in proton translocation in cytochrome c oxidase.

Mammalian mitochondrial cytochrome c oxidase catalyzes the transfer of electrons from ferrocytochrome c to molecular oxygen in the respiratory chain, while conserving the energy released during its electron transfer reactions by the vectorial movement of protons across the inner membrane of the mitochondrion. The protein domain that translocates the protons across the membrane is currently unknown. Recent research efforts have investigated the role of one of the transmembrane subunits of the enzyme (III, Mr 29,884) in the vectorial proton translocation reaction. The data that favor subunit III as integral in vectorial proton translocation as well as the data that support a more peripheral role for subunit III in proton translocation are reviewed. Possible experimental approaches to clarify this issue are presented and a general model discussed.