ELECTRON-TRANSFER FROM HIGH-POTENTIAL IRON-SULFUR PROTEIN AND LOW-POTENTIAL CYTOCHROME C-551 TO THE PRIMARY DONOR OF RUBRIVIVAX-GELATINOSUSREACTION-CENTER MUTATIONALLY DEVOID OF THE BOUND CYTOCHROME SUBUNIT

The electron transfer reactions from low-potential cytochrome c-551, h igh-potential iron-sulfur protein (HiPIP) and cytochrome c' to the pho tosynthetic reaction center mutationally devoid of the bound cytochrom e subunit in the C244 mutant of the purple bacterium Rubrivivax gelati nosus were investigated using time-resolved optical spectroscopy. Cyto chrome c-551 was the best electron donor. Both HiPIP and low-potential cytochrome c-551 can also react with the bound cytochrome subunit, bu t in this case HiPIP appeared to be more efficient than cytochrome c-5 51, Identification of soluble immediate electron donors to the bacteri ochlorophyll dimer indicates that in Rvi. gelatinosus the bound cytoch rome subunit is not essential for photosynthetic electron transport an d growth. The presence of high-and low-potential electron carriers (Hi PIP, E-m = 330 mV, and cytochrome c-551, E-m = 50 mV) involved in the reduction of the bacteriochlorophyll dimer and the bound cytochrome su bunit suggests that two alternative electron transfer pathways to the photosynthetic reaction center may exist in Rvi. gelatinosus. (C) 1997 Elsevier Science B.V.