Abstract
In a purple bacterium, Rubrivivax gelatinosus, we have shown that a high-potential iron-sulfur protein (HiPIP) is the best electron donor to the RC. Other soluble electron donors, two cytochromes c8 with different redox midpoint potentials also work as good electron donors to the RC in R. gelatinosus. To clarify the relative contributions of these three electron donors, we have constructed various mutants defective in the genes coding for these proteins. Interestingly, the triple mutant sustained photosynthetic growth ability. Flash-induced kinetic measurements using the intact cells showed photo-oxidation of a cytochrome peaking at 553 nm. The purified cytochrome had an apparent molecular weight of 25 kDa and worked as a good electron donor to the RC in reconstitution experiments. The gene coding for this cytochrome was cloned and sequenced, which has two heme-binding motifs. Mutants lacking this gene were constructed and now analysed to clarify the functions of this new cytochrome.
