THEORY OF SPECTROSCOPY AND ENERGY-TRANSFER OF OLIGOMERIC PIGMENTS IN CHLOROSOME ANTENNAS OF GREEN PHOTOSYNTHETIC BACTERIA

Evidence strongly suggests that the bacteriochlorophyll c, d, or e pigments in the chlorosome of green photosynthetic bacteria exist in a highly aggregated state, where pigment-pigment interactions are thought to dominate in determining the structural arrangement of the pigments. We have calculated the absorption spectra and fluorescence quantum yields based upon a number of proposed geometrical configurations of the in vivo and in vitro BChl aggregates as a function of aggregate size. In addition, the time-resolved fluorescence measurements are discussed and rationalized in terms of sequential energy transfer with average rate constant resulting in eventual energy flow from chlorosome to reaction center. We suggest that the observed absorption and fluorescence data result from the formation of a two-dimensional zig-zag and/or one-dimensional aggregate in vitro depending upon the solvent conditions, and a predominantly two-dimensional zig-zag structure in vivo.