Cytochrome c oxidase is not a proton pump.

We conclude that the reduction of O2 to 2 H2O by cytochrome c oxidase of rat liver mitochondria involves the translocation of 4-from cytochrome c at the outer surface of the cristae membrane per O2 reduced and protonated by 4 H+ ions that enter the reaction domain from the inner aqueous phase. This net electron-translocating function of cytochrome c oxidase plugged through the mitochondrial cristae membrane is not linked to a proton-pumping function, such as that proposed by Wikström [7,8].