Spectral and functional characterization of membrane fragments from the facultative photosynthetic bacterium Rhodopseudomonas blastica

The cytochromes of photosynthetically grown Rhodopseudomonas blastica have been thermodynamically characterized using the technique of redox titrations. Six cytochromes were present; two cytochromes c, E _m7= +295mV, E _m7=+345mV; and four cytochromes b, E _m7=+290mV, E _m7=+130mV, E _m7=+60mV, E _m7=-4mV. These cytochromes were tightly bound except for cytochrome c with E _m7 of+345mV which was mostly present in the soluble cell extracts.The effects of cyanide on both the cytochrome c oxidase activity and the NADH-dependent respiration, revealed the presence of a branched respiratory chain, one branch leading to a cyanide-resistant oxidase containing pathway and the other including the cyanide-sensitive cytochrome c-oxidase.The effects of antimycin A, myxothiazol and 5-undecyl-6-hydroxy-4,7-dioxobenzothiazole (UHDBT) on the steadystate NADH-dependent respiration were also studied. Antimycin A and myxothiazol appeared to act at the level of the ubiquinol-cytochrome c oxidoreductase while UHDBT drastically affected both respiratory branches.Absorption spectra of chromatophore photopigments resulted to be similar to those reported in many species of facultative photosynthetic bacteria although carotenoid absorption maxima were blue-shifted by 5 nm.The light-induced oxygen reduction performed by chromatophores from R. blastica suggested a strict interaction between photosynthetic and respiratory apparatuses.