A Light-Harvesting Pigment-Protein Complex Associated with the Reaction Center of Green Bacteria

Abstract

Green photosynthetic sulfur bacteria have an extensive antenna system consisting of 1000 – 2000 bacteriochlorophyll (BChl) molecules per reaction center. Most of these are BChl c, d or e, contained in the so-called chlorosomes. BChl a is situated in or close to the cytoplasmic membrane, which also contains the reaction center (Olson, 1978). Incubation of the membrane with Triton X-100 produces a pigment-protein complex (PP), that contains about 80 BChl a. per reaction center. Subsequent treatment with guanidine-HCl removes two molecules of the light-harvesting BChl a protein, each containing 21 BChl a and produces the RCPP complex (about 35 BChl a; Swarthoff, Amesz, 1979). Fluorescence emission and excitation and linear dichroism (LD) spectra indicate that the RCPP complex still contains a significant amount of BChl a protein in a bound form, in addition to a ‘core complex’, that is associated with the reaction center (Kramer et al., 1982; Swarthoff et al., 1980). In this paper we describe the isolation of this core complex and some of its properties.