Homology in the structure and the prosthetic groups between two different terminal ubiquinol oxidases, cytochrome a1 and cytochrome o, of Acetobacter aceti

Abstract

Acetobacter aceti produces two different terminal oxidases dependent on the culture conditions, shaking and static cultures. Cells grown on shaking culture contain cytochrome a1, while cytochrome o is present in cells grown on static culture. Cytochrome a1 and cytochrome o of A. aceti were compared especially with respect to the protein structure and the prosthetic groups. Cytochrome a1 exhibited lower CN sensitivity and higher affinity for O2 than cytochrome o. Both terminal oxidases consisted of four nonidentical polypeptides of which the molecular sizes were identical between both enzymes. Cytochrome a1 cross-reacted with an antibody raised against cytochrome o at the same level as cytochrome o did, and an antibody elicited against cytochrome a1 cross-reacted with both cytochrome o and cytochrome a1 at the same intensity, which indicates that both oxidases are indistinguishable immunochemically. Furthermore, almost the same peptide mapping pattern with chymotrypsin was observed in subunit I and in subunit II between both terminal oxidases, and the amino-terminal sequences in the subunit II of both oxidases were identical at least in their 10 amino acids. As for the prosthetic groups, both oxidases were shown to contain two heme-irons and one copper atom. Further, high performance liquid chromatography analysis of the heme moieties extracted from both the purified enzymes indicated that cytochrome a1 contains hemes b and a at a ratio of 1 to 1, whereas cytochrome o contains the same amounts of hemes b and o. Thus, data indicate that cytochrome a1 and cytochrome o of A. aceti are cytochrome ba and cytochrome bo ubiquinol oxidases, respectively, and that both oxidases have a closely similar protein structure and prosthetic groups, in which only heme a in the heme/copper binuclear center of cytochrome a1 is replaced by heme o in that of cytochrome o.