Primary Intermediate in the Reaction of Mixed Valence Cytochrome C Oxidase with Oxygen.

The reaction of dioxygen with mixed valence cytochrome c oxidase was followed in a rapid mixing continuous flow apparatus. The optical absorption difference spectrum and a kinetic analysis confirm the presence of the primary oxygen intermediate in the 0-100 microsecond time window. The resonance Raman spectrum of the iron-dioxygen stretching mode (568 cm sup -1) supplies evidence that the degree of electron transfer from the iron atom to the dioxygen is similar to that in oxy complexes of other heme proteins. Thus, the Fe-O sub 2 bond does not display any unique structural features which could account for the rapid reduction of dioxygen to water. Furthermore, the frequency of the iron-dioxygen stretching mode is the same as that of the primary intermediate in the fully reduced enzyme indicating that the oxidation state of cytochrome a plays no role in controlling the initial properties of the oxygen binding site.