Electrogenesis associated with proton transfer in the reaction center protein of the purple bacterium Rhodobacter sphaeroides

Abstract

Electrogenic events in the photosynthetic reaction center complex (RC), accompanying single‐ and two‐electron reduction of the secondar quinone acceptor Q_b, 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 q_a, 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.