Isolation and properties of a pigment-protein complex associated with the reaction center of the green photosynthetic sulfur bacterium Prosthecochloris aestuarii

Abstract

The membrane-bound pigment system of green sulfur bacteria consists of light-harvesting bacteriochlorophyll a-protein and a ‘core complex’ that is associated with the reaction center (Kramer, H.J.M., Kingma, H., Swarthoff, T. and Amesz, J. (1982) Biochim. Biophys. Acta 681, 359–364). The isolation and properties of the core complex from Prosthecochloris aestuarii are described. The complex has a molecular mass of 200 ± 50 kDa and contains bacteriochlorophyll a, carotenoid and pigments absorbing near 670 nm (probably bacteriopheophytin c and an unidentified pigment). Fluorescence emission spectra and sodium dodecyl sulfate polyacrylamide gel electrophoresis showed the absence of light-harvesting bacteriochlorophyll a-protein. The preparation showed no reaction center activity. Circular and linear dichroism spectra indicated that the structure of the core complex was basically not altered by the isolation procedure. Comparison with the CD spectrum of the intrinsic membrane-bound pigment-protein complex indicates that the latter contains 14 bacteriochlorophyll a molecules (two subunits) belonging to the light-harvesting protein and about 20 bacteriochlorophyll a molecules belonging to the core complex.