ИСТИНА

Molecular dynamics simulations allow direct investigation of the molecular mechanics of charge separation reactions in photosynthetic bacterial reaction center (BRC). A molecular model of BRC was developed with the aim to examine the impact of microscopic movements of protein, lipid bilayer and surrounding water on different charge transfer reactions in BRC. The primary charge separation is difficult for theoretical explication: the reaction kinetics, which does not change over a wide range of temperature and free energy, reveals oscillatory features. Here the reaction mechanism was analyzed within a phenomenological Langevin approach. The spectral function of polarization around the special pair PL/PM and the dielectric response upon the formation of PL+/PM− dipole were calculated. The system response was approximated by Langevin oscillators, the respective frequencies, friction and energy coupling coefficients were determined. The protein dynamics around PL and PM was shown to be highly asymmetric. The polarization around PL was described largely by a single Debye mode with relaxation time of 80 fs and the amplitude of 130 mV; the protein response around PM could be largely described by two oscillatory modes with frequencies of 90 and 150 cm-1 and the total amplitude of 50 mV. The revealed polarization dynamics was in agreement with the observed oscillatory behavior and could rationalize the other properties of primary charge separation. The spatially heterogeneous distribution of the dielectric permittivity in BRC was calculated using the Kirkwood-Fröhlich's approach. Based on this distribution we developed a Poisson-Boltzmann model of BRC, which included several dielectric strata; its numeric solution was in quantitative agreement with diverse experimental data obtained in our laboratory by the direct electrometric measurements. The work was supported by RSF 14-14-00789.