Purification of membrane-bound cytochromes and a photoactive P840 protein complex of the green sulfur bacterium Chlorobium limicola f. thiosulfatophilum

AbstractA photoactive P840 protein complex and a fraction enriched in cytochrome b from chromatophores of Chlorobium limicola f. thiosulfatophilum are described. The former is identical in pigment composition to the ‘core complex’ of Prostecochloris aestuarii [(1983) Biochim. Biophys. Acta 725, 361–367]. It consists of 3 major polypeptides. The dominating one, of 65 kDa and carrying bacteriochlorophyll, is the P840 reaction center protein. It is probably very similar to the P700 reaction center protein of chloroplasts and cyanobacteria. A 24-kDa protein could be identified as an ascorbate-reducible cytochrome c-550.5. The third polypeptide of 32 kDa might be a Rieske-type FeS protein. The cytochrome b fraction consists of 2 polypeptides of 42 kDa, representing cytochrome b-562, and 24 kDa, representing ascorbate-reducible cytochrome c-550.5 again. Conditions can be varied to obtain cytochrome b-562 in pure form. A first characterization of the components is presented