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 pig ments in the chlorosome of green photosynthetic bacteria exist in a hi ghly 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 yi elds 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 discusse d and rationalized in terms of sequential energy transfer with average rate constant resulting in eventual energy flow from chlorosome to re action center. We suggest that the observed absorption and fluorescenc e data result from the formation of a two-dimensional zig-zag and/or o ne-dimensional aggregate in vitro depending upon the solvent condition s, and a predominantly two-dimensional zig-zag structure in vivo.