The molecular features and catalytic activity of CuA-containing aco3-type cytochrome c oxidase from a facultative alkalophilic Bacillus.

Cytochrome aco3 of Bacillus YN-2000 was purified by an improved procedure and its molecular features and catalytic activity were extensively studied. The enzyme molecule was composed of three subunits with M(r)s of 50,000, 41,000, and 22,000, and contains 1 molecule each of cytochrome a, cytochrome c, and cytochrome o3 in the minimal structural unit (M(r), 113,000). The 41,000 subunit (subunit II) contains heme c. The EPR, optical, and resonance Raman spectra of the oxidized enzyme demonstrated the presence of CuA whose coordination environment bore close resemblance to that of the aa3-type cytochrome c oxidase. Resonance Raman studies demonstrated that the cytochrome a moiety was similar to that of an aa3-type oxidase and also that the cytochrome o3 contained a five-coordinated high-spin heme with histidine as an axial ligand. The Fe-CO stretching mode of the cytochrome o3.CO complex was observed at 520 cm-1, which is the same frequency as that of cytochrome aa3.CO. The oxygen consumption activity of cytochrome aco3 was measured using several kinds of cytochromes c as the electron mediators. The reaction between cytochrome aco3 and eucaryotic cytochromes c was completely inhibited by poly-L-lysine. In contrast, poly-L-lysine was indispensable for sufficient reaction between the oxidase and Bacillus YN-2000 cytochrome c-553, the physiological electron donor. The combined results on the structure and enzymatic properties suggest that the cytochrome aco3 is very similar to cytochrome caa3 except that the cytochrome aco3 has cytochrome o3 in place of cytochrome a3 and the cytochrome c component has a very low redox midpoint potential (95 mV).(ABSTRACT TRUNCATED AT 250 WORDS)