Primary Processes of Charge Separation in Reaction Centers of YM210L/FM197Y and YM210L Mutants of Rhodobacter sphaeroides

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A. G. Yakovlev^1*, L. G. Vasilieva², A. Y. Shkuropatov², and V. A. Shuvalov^1,2

¹Department of Photobiophysics, Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119991 Moscow, Russia; fax: (495) 939-3181; E-mail: yakov@genebee.msu.su

²Institute of Basic Biological Problems, Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russia; fax: (496) 779-0532; E-mail: shuvalov@issp.serpukhov.su

^* To whom correspondence should be addressed.

Received March 12, 2009; Revision received May 18, 2009

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Difference femtosecond absorption spectroscopy with 20-fsec temporal resolution was applied to study a primary stage of charge separation and transfer processes in reaction centers of YM210L and YM210L/FM197Y site-directed mutants of the purple bacterium Rhodobacter sphaeroides at 90 K. Photoexcitation was tuned to the absorption band of the primary electron donor P at 880 nm. Coherent oscillations in the kinetics of stimulated emission of P* excited state at 940 nm and of anion absorption of monomeric bacteriochlorophyll B_A^– at 1020 nm were monitored. The absence of tyrosine YM210 in RCs of both mutants leads to strong slowing of the primary reaction P* → P⁺B_A^– and to the absence of stabilization of separated charges in the state P⁺B_A^–. Mutation FM197Y increases effective mass of an acetyl group of pyrrole ring I in the bacteriochlorophyll molecule P_B of the double mutant YM210L/FM197Y by a hydrogen bond with OH-TyrM197 group that leads to a decrease in the frequency of coherent nuclear motions from 150 cm^–1 in the single mutant YM210L to ~100 cm^–1 in the double mutant. Oscillations with 100-150 cm^–1 frequencies in the dynamics of the P* stimulated emission and in the kinetics of the reversible formation of P⁺B_A^– state of both mutants reflect a motion of the P_B molecule relatively to P_A in the area of mutual overlapping of their pyrrole rings I. In the double mutant YM210L/FM197Y the oscillations in the P* emission band and the B_A^– absorption band are conserved within a shorter time ~0.5 psec (1.5 psec in the YM210L mutant), which may be a consequence of an increase in the number of nuclei forming a wave packet by adding a supplementary mass to the dimer P.

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KEY WORDS: photosynthesis, charge separation, reaction center, wave packet, electron transfer

DOI: 10.1134/S0006297909110042

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