A Functional Model of Cytochrome c Oxidase: Thermodynamic Implications

The environment of the CuI ion in the distal ligand group decides the fate of the reduction of O2 by the two analogues 1 and 2 of the heme a3 CuB center in cytochrome c oxidase. The fourfold coordination by N in 1 favors the CuII oxidation state and leads to a 4 e−–4 H+ reduction and the formation of H2O under physiological conditions, while with 2 a 2 e−–2 H+ reduction occurs to form the cytotoxic H2O2.