Energy transfer pathways in reaction centre upon femtosecond excitation ofaccessory bacteriochlorophylls

The energy transfer pathways from the excited accessory bacteriochlorophyll s (B*) within native and modified (pheophytin-exchanged) reaction centres i solated from Rhodobacter sphaeroides (RS601) have been investigated by usin g the femtosecond pump-probe technique. For native RS601, B* decays with a time constant of 240 fs, followed by a partial recovery of the ground-state bleaching with a timescale of about 2 ps. In modified RS601 (Phe), however , B* decays with a time constant of 800Es for magic angle (54.7 degrees) po larization configuration. In addition to the general assumption of energy t ransfer pathway from B* to the special pair P, an alternative pathway for e nergy transfer probably operates as well.