In vitro and in vivo electron transfer to the triheme cytochrome subunit bound to the photosynthetic reaction center complex in the purple bacterium Rhodovulum sulfidophilum

AbstractThe cytochrome subunit bound to the photosynthetic reaction center (RC) complex in Rhodovulum sulfidophilum lacks one heme-binding motif (CXXCH) out of four motifs found in other purple bacteria resulting in the absence of the most distal heme from the RC-core complex (S. Masuda et al., J. Biol. Chem. 274 (1999) 10795). Cytochrome c2, which acts as the electron donor to the RC was purified, and its gene was cloned and sequenced. The redox midpoint potential of cytochrome c2 was determined to be Em=357 mV. The photo-oxidation and re-reduction of purified cytochrome c2 were observed in the presence of membrane preparations. Flash-induced photo-oxidation and re-reduction of the RC-bound cytochrome were also observed in intact cells. Despite the unusual nature of the RC-bound cytochrome subunit, the cyclic electron transfer system in Rdv. sulfidophilum was shown to be similar to those in other purple bacteria