THE SEQUENCE OF ELECTRON CARRIERS IN THE REACTION OF CYTOCHROME-C-OXIDASE WITH OXYGEN

Kinetic studies of the electron transfer processes performed by cytochrome oxidase have assigned rates of electron transfer between the metal centers involved in the oxidation of ferrocytochrome c by molecular oxygen. Transient-state studies of the reaction with oxygen have led to the proposal of a sequence of carriers from cytochrome c, to Cu(A), to cytochrome a, and then to the binuclear (i.e., cytochrome a3-Cu(B)) center. Electron exchange rates between these centers agree with relative center-to-center distances as follows; cytochrome C to Cu(A) 5-7 angstrom, cytochrome c to cytochrome a 20-25 angstrom, Cu(A) to cytochrome a 14-16 angstrom and cytochrome a to cytochrome a3-Cu(B) 8-10 angstrom. It is proposed that the step from cytochrome a to the binuclear center is the key control point in the reaction and that this step is one of the major points of energy transduction in the reaction cycle.