Bound cytochrome C as proton donor and acceptor during enzymic oxidoreduction.

Abstract When ferrocytochrome c reacts with delipidated cytochrome oxidase under conditions which prevent oxidation, one proton is taken up per molecule of ferrocytochrome c bound to cytochrome oxidase. When ferricytochrome c reacts with delipidated Complex III, one proton is released per molecule of ferricytochrome c bound to Complex III. From these data it can be concluded that the oxidation of ferrocytochrome c by cytochrome oxidase leads to the release of a proton and an electron, whereas the reduction of ferricytochrome c by Complex III leads to the uptake of a proton and an electron. Thus ferrocytochrome c like QH 2 and NADH is both an electron and proton donor, and ferricytochrome c like Q and O 2 is both an electron and proton acceptor. The pattern for the three mitochondrial electron transfer sequences NADH → Q, QH 2 → ferricytochrome c and ferrocytochrome c → O 2 involves separation of an electron and proton on the side of the membrane where electron transfer is initiated and recombination of an electron and a proton in the terminal acceptor on the side of the membrane where electron transfer terminates.