Efficient energy transfer from the carotenoid S-2 state in a photosynthetic light-harvesting complex

Previously, the spatial arrangement of the carotenoid and bacteriochlorophy ll molecules in the peripheral light-harvesting (LH2) complex from Rhodopse udomonas acidophila strain 10050 has been determined at high resolution. He re, we have time resolved the energy transfer steps that occur between the carotenoid's initial excited state and the lowest energy group of bacterioc hlorophyll molecules in LH2. These kinetic data, together with the existing structural information, lay the foundation for understanding the detailed mechanisms of energy transfer involved in this fundamental, early reaction in photosynthesis. Remarkably, energy transfer from the rhodopin glucoside S-2 state, which has an intrinsic lifetime of similar to 120 fs, is by far the dominant pathway, with only a minor contribution from the longer-lived S-1 state.