Abstact

Fully oxidized cytochrome c oxidase (CcO) under enzymatic turnover is capable of pumping protons, while fully oxidized CcO as isolated is not able to do so upon one-electron reduction. The functional difference is expected to be a consequence of structural differences: [Fe(3+)-OH(-)] under enzymatic turnover versus [Fe(3+)-O(2)(2-)-Cu(2+)] for the as-isolated CcO. However, the electron density for O(2)(2-) is equally assignable to Cl(-). An anomalous dispersion analysis was performed in order to conclusively demonstrate the absence of Cl(-) between the Fe(3+) and Cu(2+). Thus, the peroxide moiety receives electron equivalents from cytochrome c without affecting the oxidation states of the metal sites. The metal-site reduction is coupled to the proton pump.