Examination of the functional roles of 5 highly conserved residues in the cytochrome b subunit of the bc sub(1) complex of Rhodobacter sphaeroides

The cytochrome b subunit of the bc sub(1) complexes contains two cytochrome components (b sub(L) and b sub(H)) and is the locus of both a quinol-oxidizing site (Q sub(o) or Q sub(z)) and a quinone-reducing site (Q sub(i) or Q sub(c)). Sequence alignments of this subunit from over 20 eukaryotic and prokaryotic species have revealed a remarkable degree of conservation, including approximately 20 totally conserved residues. In this paper, site-directed mutagenesis has been used to examine the structural or functional roles of 5 of these highly conserved residues, Gly super(48), Gln super(58), Ser super(102), Phe super(104), and Pro super(202), all predicted to be within transmembrane alpha -helical segments. The mutants were made in the bc sub(1) complex of Rhodobacter sphaeroides), a photosynthetic bacterium.