Characterization of mutations in the cytochrome b subunit of the bc1 complex of Rhodobacter sphaeroides that affect the quinone reductase site

The effect of site-specific mutations on the cytochrome b subunit of the bc1 complex of Rhodobacter sphaeroides was investigated. Mutation was aimed at the residues which were in proximity to the quinone reductase site. REsults indicated that the mutants maintained a functional quinol oxidizing site although the rate of cytochrome bh reoxidation was variably affected. A critical defect was observed in the bc1 complex due to deficient reoxidation of cytochrome bh by ubiquinone. This in turn, impedes electron transport through the cytochromes.