Mechanism of Dioxygen Reduction by Cytochrome c Oxidase as Studied by Time-Resolved Resonance Raman Spectroscopy

Time-resolved resonance Raman (TR3) spectroscopy has been applied to cytochrome c oxidase (CcO) to elucidate the mechanism of dioxygen reduction. Six oxygen isotope-sensitive Raman bands have been identified in the TR3 spectra. The “607-nm species” defined by difference absorption spectrum, which is referenced against the oxidized enzyme, is demonstrated to have an Fe=O heme, although it has long been believed to have an Fe-O-O-X (X=H or CuB) heme. The one-electron reduction of this Fe=O intermediate, which yields the oxoferryl intermediate, is demonstrated to be coupled with proton transfer in the protein. The mechanism of dioxygen reduction by CcO is discussed on the basis of the structures of the reaction intermediates.