Abstract
Cytochrome c oxidase having heme O in addition to heme C and heme A (cytochrome cao) [Sone, N., & Fujiwara, Y. (1991) FEBS Lett. 288, 154-158] was isolated from a thermophilic bacterium, Bacillus PS3, grown under slightly air-limited conditions. Cytochrome cao could oxidize yeast cytochrome c and N,N,N',N'-tetramethyl-p-phenylenediamine twice as fast as cytochrome caa3, which this organism yielded under normal growing conditions. Cytochrome cao also pumped protons upon cytochrome c oxidation in a way similar to cytochrome caa3. Binding of cyanide to cytochrome cao caused spin-state conversion of heme O at the binuclear center and seriously inhibited its physiological activity. A low Ki value (0.4 microM) for cyanide was found to be mainly due to a small "off" constant. Resonance Raman spectra of cytochrome cao bore close resemblance to those of cytochrome caa3 in both oxidized and reduced states, although the formyl stretching (vCH=O) band was absent. The Fe-histidine stretching (vFe-His) and Fe-CO stretching (vFe-CO) frequencies of cytochrome cao were very close to those seen for cytochrome caa3, but were distinct from those of hemoglobin and peroxidases, suggesting that the protein structure in the vicinity of heme O resembles that of the heme a3 moiety of cytochrome caa3.
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