Resonance Raman spectra of cytochrome c oxidase. Excitation in the 600-nm region

Abstract

The resonance Raman (RR) spectra of oxidized, reduced and oxidized cyanide-bound cytochrome c oxidase [from beef heart] with excitation at several wavelengths in the 600 nm region are presented. No evidence is found for laser-induced photoreduction of the oxidized protein with irradiation at .lambda. .apprx. 600 nm at 195.degree. K, in contrast to the predominance of this process upon irradiation in the Soret region at this temperature. The Raman spectra of all 3 protein species are very similar, and there are no Raman bands which are readily assignable to either cytochrome a or cytochrome a3, exclusively. The Raman spectra of the 3 protein species exhibit a number of bands not observed in the RR spectra of other hemoproteins upon excitation in their visible absorptive bands. In particular, strong Raman bands are observed in the low-frequency region of the RR spectra (< 500 cm-1). The frequencies of these bands are similar to those of the Cu ligand vibrations observed in the RR spectra of type 1 Cu proteins upon excitation in the 600 nm absorption band characteristic of these proteins. In cytochrome c oxidase, these bands do not disappear upon reduction of the protein and, therefore, cannot be attributed to Cu-ligand vibrations. Thus, all the observed RR bands are associated with the 2 heme A moieties in the enzyme.