Raman spectra of heme a, cytochrome oxidase-ligand complexes, and alkaline denatured oxidase

Abstract

The 441.6 nm excitation resonance Raman spectra of oxidized and reduced monomeric heme a-imidazole, cytochrome oxidase-exogenous ligand complexes in various redox states, and alkaline denatured oxidase are reported. In reduced oxidase, the cytochrome a3 Raman spectrum has bands at 215, 364, 1230 and 1670 cm-1 not observed in the cytochrome a spectrum. The appearance of these bands in the reduced cytochrome a3 spectrum is due to interactions between the heme a of cytochrome a3 and its protein environment and not to intrinsic properties of heme a. These interactions are pH sensitive and strongly influence the vibrational spectra of both heme a groups. The 1670 cm-1 band is assigned to the heme a formyl substituent, the intensity of the 1670 cm-1 is probably high for reduced cytochrome a3 because the C.dbd.O lies in the porphyrin plane and is very weak for oxidized and reduced cytochrome a, oxidized cytochrome a3, and oxidized and reduced heme a-imidazole because the C.dbd.O lies out of the plane. Movement of the C.dbd.O in and out of the plane may explain the ligand induced spectral shift in the optical absorption spectrum of reduced cytochrome a3. The observation of Adar and Yonetani, under laser illumination, resting oxidase is photoreactive, is confirmed.