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

The cytochrome subunit bound to the photosynthetic reaction center (RC) com plex in Rhodovulum sulfidophilum lacks one heme-binding motif (CXXCH) out o f four motifs found in other purple bacteria resulting in the absence of th e most distal heme from the RC-core complex (S. Masuda et al., J. Biol. Che m. 274 (1999) 10795). Cytochrome c(2), which acts as the electron donor to the RC was purified, and its gene was cloned and sequenced. The redox midpo int potential of cytochrome c(2) was determined to be E-m = 357 mV. The pho to-oxidation and re-reduction of purified cytochrome c(2) 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. D espite the unusual nature of the RC-bound cytochrome subunit, the cyclic el ectron transfer system in Rdv. sulfidophilum was shown to be similar to tho se in other purple bacteria. (C) 2001 Elsevier Science B.V. All rights rese rved.