Electron transfer between cytochrome c and the binuclear center of cytochrome oxidase.

The Minnaert model, which can account for the reaction kinetics between cytochrome oxidase and cytochrome c (Cytc), has been used to justify equal binding rate constants for reduced and oxidized Cytc. Here we extend the model beyond reversible binding of Cytc and its irreversible oxidation to include CuA, heme a and the oxidation cycle of the binuclear center. The model reproduces the experimental reduction of CuA and heme a during turnover and the low population of the ferryl and ferrous heme a3. It predicts that the off rate constants for reduced and oxidized Cytc can be unequal and that the non-Nernst response of CuA and heme a is due to disequilibrium between free Cytc and CuA rather than redox anticooperativity.