A membrane-bound electron donor cytochrome to the reaction center-bound cytochrome subunit of the purple photosynthetic bacterium, Rhodovulum sulfidophilum

Abstract

Photosynthetic membranes free from soluble proteins were prepared from spheroplasts of the purple bacterium, Rhodovulum sulfidophilum which has the RC-bound cytochrome subunit lacking one of the hemes, heme-1. Upon flash excitation of this membrane, a rapid re-reduction of the photooxidized RC-bound cytochrome was observed, suggesting that a membrane-bound electron donor to the RC is included in the photosynthetic electron transfer pathways of Rdv. sulfidofilum. From membranes of Rdv. sulfidofilum, a 100-kDa cytochrome c was solubilized with low concentration (30mM) of octylthioglucoside. This cytochrome c reduced the photooxidized RC-bound cytochrome in vitro, suggesting that this cytochrome c was the membrane-bound electron donor mentioned above. This is the first example of the membrane-bound major electron donor to the RC in purple bacteria which have the RC-bound cytochrome subunit.