H2O2‐Induced Conversion of Cytochrome c Oxidase Peroxy Complex to Oxoferryl State

Abstract

Addition of high H2O2 concentrations to a peroxy complex of proteoliposome-bound cytochrome oxidase converts the complex to a spectrally distinct species. The difference spectrum of the high-peroxide compound versus the oxidized enzyme is characterized in a visible range by a broad symmetrical band at 580 nm (delta epsilon approximately equal to 4 mM-1 cm-1) with a minor second maximum at approximately 535 nm; a complete disappearance of the 605-607-nm peak occurs which is typical of the peroxy complex. In the Soret band, the spectrum of the high H2O2 compound is virtually indistinguishable from that of the initial peroxide adduct. The high-peroxide compound appears to be identical with an oxoferryl intermediate formed in the forward and reversed cytochrome oxidase reaction. The transition of the peroxy complex to the oxoferryl state is favored by alkaline pH and counteracted by ferricyanide. The peroxy and oxoferryl complexes of cytochrome c oxidase can also be formed with t-butylhydroperoxide.