REVERSIBLE OXIDATION OF ANTENNA BACTERIOCHLOROPHYLL IN TWO PHOTOREACTION CENTERLESS MUTANTS OF RHODOSPIRILLVM RUBRUM

Abstract— Reversible oxidation of bacteriochlorophyll in two independent mutants of Rhodospirillum rubrum lacking photoreaction center has been studied to obtain further information about the antenna system of that bacterium. Oxidation of antenna bacteriochlorophyll with ferricyanide is accompanied by three distinct absorbance changes in the near infrared: the appearance of a new band at 1230 nm (B1230) and the bleaching of two bands, a major one at 882 nm (B882) and a minor one at 888 nm (B888). The three absorbance changes take place at potentials higher than those required for complete oxidation of photoreaction-center bacteriochlorophyll in wild-type strains. On the other hand, the B882 bleaching and the B1230 appearance occur under similar redox conditions. The above data suggest, first, that in Rds. rubrum , contrary to the current generalized idea, antenna bacteriochlorophyll exhibits at least two absorption bands, B888 and B882; second, that B882 and B1230 correspond to the same bacteriochlorophyll component. In addition, the appearance of B1230 may indicate that antenna bacteriochlorophyll can be partially arranged in an oligomeric fashion, for bands in that spectral region are not exhibited by oxidized monomeric bacteriochlorophyll.