THE CBB(3)-TYPE CYTOCHROME-C-OXIDASE FROM RHODOBACTER-SPHAEROIDES, A PROTON-PUMPING HEME-COPPER OXIDASE

Rhodobacter sphaeroides expresses a bb(3)-type quinol oxidase, and two cytochrome c oxidases, cytochrome aa(3) and cytochrome cbb(3). We rep ort here the characterization of the genes encoding this latter oxidas e. The ccoNOQP gene cluster of R. sphaeroides contains four open readi ng frames with high similarity to all ccoNOQP/fixNOQP gene clusters re ported so far. CcoN has the six highly conserved histidines proposed t o be involved in binding the low spin heme, and the binuclear center m etals. ccoO and ccoP code for membrane bound mono- and diheme cytochro mes c. ccoQ codes for a small hydrophobic protein of unknown function. Upstream from the cluster there is a conserved Fnr/FixK-like box whic h may regulate its expression. Analysis of a R. sphaeroides mutant in which the ccoNOQP gene cluster was inactivated confirms that this clus ter encodes the cbb(3)-type oxidase previously purified. Analysis of p roton translocation in several strains shows that cytochrome cbb(3) is a proton pump. We also conclude that cytochromes cbb(3) and aa(3) are the only cytochrome c oxidases in the respiratory chain of R sphaeroi des. (C) 1998 Elsevier Science B.V. All rights reserved.