Oxygen intermediates and mixed valence states of cytochrome oxidase: infrared absorption difference spectra of compounds A, B, and C of cytochrome oxidase and oxygen.

Abstract

A study of the near IR absorption spectra of 3 O compounds of beef heart membrane-bound cytochrome oxidase (ferrocytochrome c:oxygen oxidoreductase; EC 1.9.3.1) shows that the formation of compound A (oxycytochrome oxidase) causes no significant IR absorbance changes at -103.degree. C. At -64.degree. C, the formation of compound C from the mixed-valence state of the oxidase leads to increased absorption at 740-750 nm. The formation of compound B at -84.degree. C from the fully reduced state of the oxidase causes increased absorption at 790-800 nm. Further oxidation of cytochrome oxidase results in increased IR absorption at 820-830 nm at -60.degree. C. The position of the IR absorption band in compound C thus depends at least upon the oxidation-reduction state of heme a and its associated Cu atom. Compound C contains 2 types of oxidized (cupric) Cu; that associated with heme a is initially oxidized, and that associated with heme a3 is oxidized as a 2nd step in the reaction with O. Compound C exhibits a unique intense absorption band at 606-609 nm that is tentatively assigned to a charge transfer interaction between heme a3 in the reduced state and its associated Cu in the oxidized state, with heme a and its associated Cu in the oxidized state.