ELECTROGENESIS ASSOCIATED WITH PROTON-TRANSFER IN THE REACTION CENTER PROTEIN OF THE PURPLE BACTERIUM RHODOBACTER-SPHAEROIDES

Electrogenic events in the photosynthetic reaction center complex (RC), accompanying single- and two-electron reduction of the secondar quinone acceptor Qb, were investigated. In the presence of inhibitors of electron transfer via the bc1-complex, the kinetics of formation of the transmembrane electric potential difference induced by two successive light flashes exhibit a few phases. Besides the fast phase A which is due to the charge separation between the bacteriochlorophyll dimer P and primary quinone acceptor qa, two slower atrazine-sensitive phases, BI and BII, were observed. Phase BI is suggested to be due to proton transfer between the amino acid residues of the reaction center protein, and phase BII due to proton uptake during the second flash-induced formation of ubiquinol. A possible model of electrogenesis in the acceptor moiety of the RC is discussed. © 1990.