The location of CuA in mammalian cytochrome c oxidase

Imposition of a protonmotive force across the inner membrane of coupled cyanide-inhibited, beef heart mitochondria by addition of ATP causes reduction of cytochrome c and CuA with concomitant oxidation of haem aA. The data are consistent with previous demonstrations of an intramembrane location of haem aA but further indicate that CuA is very close to the cytosolic surface of the membrane. The implications of this finding for electron transfer route and the site of the proton pumping chemistry are discussed.