Electron transfer from high-potential iron-sulfur protein and low-potential cytochrome c-551 to the primary donor of Rubrivivax gelatinosus reaction center mutationally devoid of the bound cytochrome subunit

Abstract

The electron transfer reactions from low-potential cytochrome c-551, high-potential iron-sulfur protein (HiPIP) and cytochrome c′ to the photosynthetic reaction center mutationally devoid of the bound cytochrome subunit in the C244 mutant of the purple bacterium Rubrivivax gelatinosus were investigated using time-resolved optical spectroscopy. Cytochrome c-551 was the best electron donor. Both HiPIP and low-potential cytochrome c-551 can also react with the bound cytochrome subunit, but in this case HiPIP appeared to be more efficient than cytochrome c-551. Identification of soluble immediate electron donors to the bacteriochlorophyll dimer indicates that in Rvi. gelatinosus the bound cytochrome subunit is not essential for photosynthetic electron transport and growth. The presence of high- and low-potential electron carriers (HiPIP, E m=330 mV, and cytochrome c-551, E m=50 mV) involved in the reduction of the bacteriochlorophyll dimer and the bound cytochrome subunit suggests that two alternative electron transfer pathways to the photosynthetic reaction center may exist in Rvi. gelatinosus.