A Functional Model of Cytochrome c Oxidase: Thermodynamic Implications

The environment of the Cu ^I 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 Cu_B center in cytochrome c oxidase. The fourfold coordination by N in 1 favors the Cu^II 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.