Resonance Raman spectroscopic study of the caa₃ oxidase from Thermus thermophilus

The terminal caa₃ oxidase of Thermus thermophilus has been studied by resonance Raman spectroscopy. Using different excitation wavelengths in the Soret band region, it was possible to disentangle the resonance Raman spectra of the fully oxidized and fully reduced state in terms of the component spectra of the individual hemes a, a₃, and c. For the heme a and a₃ groups, the spectra reveal only minor differences compared to those of beef heart cytochrome c oxidase attributable to subtle modifications of the heme environment. These differences are not more pronounced than those between the oxidases from beef heart and Paracoccus denitrificans confirming the view that this oxidase of Th. thermophilus is a typical member of the aa₃ oxidase superfamily. The heme c component spectra display far-reaching similarities with those of c-type cytochromes which serve as mobile electron carriers in the respiratory chain. These results imply that caa₃ oxidase represents an integrated version of the noncovalent redox complex between cytochrome c and cytochrome c oxidase in higher organisms. On the other-hand, the structural changes of cytochrome c in the noncovalent complex have no counterpart in the heme c component of the caa₃ oxidase indicating a specific cytochrome c binding site for the mitochondrial enzyme.