Electrogenic proton exchange between cytochromea3active center and M-aqueous phase

Abstract

The rate of cyanide binding with the oxidized cytochrome-c oxidase in proteoliposomes is controlled by ionization of a protein group with pK~6.7, the ligand reacting with the protonated enzyme only [(1983) Bioorg. Chem. (USSR) 9,216-227]. As shown here, the kinetics of cyanide binding depends on the pH inside the proteoliposomes. The reaction rate is affected by the electrical potential difference across the proteoliposome membranes as if the a ₃-linked ionizable group exchanged H⁺ with the proteoliposome interior electrogenically. The data corroborate a hypothesis on the existence of a proton well communicating cytochrome oxidase O₂-reducing center with the M-aqueous phase.