Energy transfer within the isolated B875 light-harvesting pigment-protein complex of Rhodobacter sphaeroides at 77 K studied by picosecond absorption spectroscopy

Abstract

The energy transfer dynamics at 77 K within detergent solubilized and purified preparations of the B875 pigment-protein complex of Rhodobacter sphaeroides have been investigated by picosecond absorption spectroscopy. Isotropic absorption recovery and decay of induced absorption anisotropy provide clear evidence that B875 is inhomogeneous in these preparations. We interpret the results as fast (τ = 15 ± 5 ps) energy transfer from the major BChl 875 pigments to a minor pigment pool, B896. The excited state of B896 decays with a time constant of 650 ± 50 ps. We suggest that B896 is intrinsic to B875 complexes and exists in a highly organized state, close to the reaction center. In the intact membrane, B896 may concentrate excitation energy in the vicinity of the reaction center special pair, thereby increasing the efficiency of the final energy transfer step.