Nuclear wavepacket motion producing a reversible charge separation in bacterial reaction centers

The excitation of bacterial reaction centers (RCs) at 870 nm by 30 fs pulse s induces the nuclear wavepacket motions on the potential energy surface of the primary electron donor excited state P*, which lead to the fs oscillat ions in stimulated emission from P* [M.H. Vos, M.R. Jones, C.N. Hunter, J. Breton, J.-C, Lambry and J.-L, Martin (1994) Biochemistry 33, 6750-6757] an d in Q(Y) absorption band of the primary electron acceptor, bacteriochlorop hyll monomer B-A [A.M. Streltsov, S.I.E. Vulto, A.Y. Shkuropatov, A.J. Hoff , T.J. Aartsma and V.A. Shuvalov (1998) J. Phys. Chem. B 102, 7293-7298] wi th a set of fundamental frequencies in the range of 10-300 cm(-1). We have found that in pheophytin-modified RCs, the fs oscillations with frequency a round 130 cm(-1) observed in the P*-stimulated emission as well as in the B -A absorption band at 800 nm are accompanied by remarkable and reversible f ormation of the 1020 nm absorption band which is characteristic of the radi cal anion band of bacteriochlorophyll monomer B-A(-). These results are dis cussed in terms of a reversible electron transfer between P* and B-A induce d by a motion of the wavepacket near the intersection of potential energy s urfaces of P* and P+BA-, when a maximal value of the Franck-Condon factor i s created. (C) 2000 Federation of European Biochemical Societies.