CHARACTERIZATION OF AN IMPROVED REACTION CENTER PREPARATION FROM THE PHOTOSYNTHETIC GREEN SULFUR BACTERIUM CHLOROBIUM CONTAINING THE FES CENTERS F(A) AND F(B) AND A BOUND CYTOCHROME SUBUNIT

A photosynthetic reaction center complex was prepared from the green sulfur bacterium Chlorobium by solubilization of chlorosome-depleted membranes with lauryl maltoside, followed by anion-exchange chromatography and molecular sieve chromatography. The purified complex was characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, optical spectroscopy, and EPR spectroscopy. The major bands migrated at apparent molecular masses of 50, 42, and 32 kDa (heme-staining) and additional weaker bands at 22, 15, and 12 kDa. The isolated reaction center complex contained about 40 bacteriochlorophyll a molecules per primary electron donor, P840, assayed by photooxidation. It was competent in stable low-temperature photoreduction of the FeS centers F(A) and F(B). The spectra of these acceptors and their low-temperature photochemistry in the purified complex were the same as found in intact Chlorobium membranes and similar to what had been described for photosystem I from plants. Membrane-bound cytochrome c553 copurified with the reaction center complex. A ratio of about four hemes per P840 was determined. This result indicates that cytochrome c553 that is closely associated with the reaction center is a tetraheme cytochrome, as described for some purple bacteria.