Electron transfer to the reaction center-bound cytochrome subunit from membrane-bound electron donor of the purple photosynthetic bacterium Rhodovulum sulfidophilum

Abstract

Rhodovulum sulfidophilum has cytochrome c₂ and cytochrome c-549 as electron donors to the reaction center, and cytochrome c-549 was suggested to be the main donor. However, cytochrome c-549 appeared only in the stationary phase of growth. Since cytochrome c-549 showed a similar band pattern to that of a membrane-bound electron donor in Rhodobacter capsulatus in SDS-PAGE, it was considered that c-549 was originated from a membrane-bound component by a proteinase cleavage. To investigate if a membrane-bound component is working as the electron donor to the reaction center-bound cytochrome in this species, membranes free from water-soluble components were prepared from spheroplasts. In the prepared membranes, a rapid re-reduction of cytochrome in the reaction center complex was observed after flash-induced oxidation. The re-reduction of cytochrome in membranes free from soluble components strongly suggests that a membrane-bound electron donor is working in this bacterium.