The Isolation and Characterization of a Photochemically Active Complex from Chloropseudomonas ethylica

Abstract

A photochemically active subcellular fraction has been isolated from the green bacterium Chloropseudomonas ethylica. It is enriched in bacteriochlorophyll a and contains only a small amount of Chlorobium chlorophyll. Both a reaction-center bleaching (P840) and a cytochrome oxidation (C553) are observed to occur in the fraction. Particles that are contained in the fraction are larger than 1.5 × 106 daltons and exhibit a range of sizes consistent with some form of polymeric association of similar subunits. Around 80 bacteriochlorophyll a molecules are present per P840. In an intact photosynthetic apparatus there are about 1000-1500 total chlorophylls (including Chlorobium chlorophyll) per reaction center.The redox potentials of the reaction center P840 and C553 were found to be 0.24 and 0.17 V, respectively, in one-electron reactions. The potentials of these components are around 0.2 V lower than comparable components found in other photosynthetic organisms.