FLASH-INDUCED ELECTROGENIC REACTIONS IN THE SA(L223) REACTION-CENTER MUTANT IN RHODOBACTER-SPHAEROIDES CHROMATOPHORES

The charge transfer events in the SA(L223) reaction center mutant Rhod obacter sphaeroides chromatophores were investigated by direct electro metry. Besides the primary charge separation, the small stigmatellin-s ensitive electrogenic reaction due to the electron transfer from the p rimary to the secondary quinone acceptor in the reaction center comple x was observed after the first hash. The second flash-induced electrog enic phase of the secondary quinone protonation and subsequent electro genic reactions of the cytochrome be, complex were much slower than th ose in chromatophores of the wild type. It is suggested that replaceme nt of Ser-L223 by Ala impairs both specific proton-conducting pathways leading to the secondary quinone Q(B).