2Institute of Basic Biological Problems, Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russia; fax: (496) 773-0532; E-mail: email@example.com
* To whom correspondence should be addressed.
Received April 18, 2011; Revision received May 19, 2011
Primary stage of charge separation and transfer of charges was studied in reaction centers (RCs) of point mutants LL131H and LL131H/LM160H/FM197H of the purple bacterium Rhodobacter sphaeroides by differential absorption spectroscopy with temporal resolution of 18 fsec at 90 K. Difference absorption spectra measured at 0-4 psec delays after excitation of dimer P at 870 nm with 30 fsec step were obtained in the spectral range of 935-1060 nm. It was found that a decay of P* due to charge separation is considerably slower in the mutant RCs in comparison with native RCs of Rba. sphaeroides. Coherent oscillations were found in the kinetics of stimulated emission of the P* state at 940 nm. Fourier analysis of the oscillations revealed a set of characteristic bands in the frequency range of 20-500 cm–1. The most intense band has the frequency of ~130 cm–1 in RCs of mutant LL131H and in native RCs and the frequency of ~100 cm–1 in RCs of the triple mutant. It was found that an absorption band of bacteriochlorophyll anion BA– which is registered in the difference absorption spectra of native RCs at 1020 nm is absent in the analogous spectra of the mutants. The results are analyzed in terms of the participation of the BA molecule in the primary electron transfer in the presence of a nuclear wave packet moving along the inharmonic surface of P* potential energy.
KEY WORDS: photosynthesis, charge separation, reaction center, wave packet, electron transfer