ENERGY TRANSFERS IN THE B808-866 ANTENNA FROM THE GREEN BACTERIUM CHLOROFLEXUS-AURANTIACUS

Energy transfers within the B808-866 BChl a antenna in chlorosome-memb rane complexes from the green photosynthetic bacterium Chloroflexus au rantiacus were studied in two-color pump-probe experiments at room tem perature. The steady-state spectroscopy and protein sequence of the B8 08-866 complex are reminiscent of well-studied LH2 antennas from purpl e bacteria. B808-->B866 energy transfers occur with similar to 2 ps ki netics; this is slower by a factor of similar to 2 than B800-->B850 en ergy transfers in LH2 complexes from Rhodopseudomonas acidophila or Rh odobacter sphaeroides. Anisotropy studies show no evidence for intra-B 808 energy transfers before the B808-->B866 step; intra-B866 processes are reflected in 350-550 fs anisotropy decays. Two-color anisotropies under 808 nm excitation suggest the presence of a B808-->B866 channel arising either from direct laser excitation of upper B866 exciton com ponents that overlap the B808 absorption band or from excitation of B8 66 vibronic bands in nontotally symmetric modes.