What is the essential proton-translocating molecular machinery in cytochrome oxidase?

Pulses of O2 added to anaerobic mitochondria in the presence of antimycin, but in the absence of exogenous reductants, led to H+ translocation until the amount of oxidizing equivalents exceeded the number of endogenous reducing equivalents capable of rapid reduction of cytochrome oxidase. This demonstrates that either the heme of cytochrome alpha or that CuA is the redox center, the function of which is coupled to proton translocation in cytochrome oxidase. Chemical labeling of subunit III of cytochrome oxidase by dicyclocarbodiimide (DCCD), or removal of this subunit by treatment of the enzyme at high pH, results in loss of proton translocation by the isolated and membrane-reconstituted enzyme. Possible roles of subunit III in proton translocation are discussed.