MEMBRANE-BOUND CYTOCHROME c (100 KDA) WORKING AS AN ELECTRON DONOR TO THE REACTION CENTER IN THE PURPLE BACTERIUM, RHODOVULUM SULFIDOPHILUM

摘要

The reaction center (RC) complex of most purple bacteria consists of L, M, H and tetraheme cytochrome subunits. The cytochrome subunit works as the immediate electron donor to the photooxidized special pair of bacteriochrolophylls in the membrane-spanning LM core complex. The oxidized hemes in this subunit are rereduced by soluble electron carriers such as cytochrome c_2. Studies employing site-directed mutagenesis to the cytochrome subunit have shown that the direct electron acceptor from the soluble electron carriers is the most distal heme (heme-1) from the special pair (Osyczka et al 1998). Recently we found an unusual cytochrome subunit in a marine purple bacterium, Rhodovulum sulfidophilum, in which the heme corresponding to heme-1 was missing (Masuda et al 1999). It was suspected that Rdv. sulfidophilum has a unique pathway of photosynthetic electron transfer through the unusual "triheme" cytochrome subunit.