ИСТИНА

Ion-radical pair P870+ •QA• in the reaction centers (RC) structure is the source of the electric field influence on the charged groups of the protein, changing their spatial orientation. Indirectly this influence should be manifested in the fluorescence characteristics of tryptophan residues, which are internal indicator of the dynamic state of the RC protein. In this investigation the temperature dependence of the recombination rate of charges separated between the photoactive bacteriochlorophyll P and primary quinone acceptor QA in the photosynthetic RC from purple bacteria Rhodobacter sphaeroides were studied. Recombination kinetics were measured in the individual absorption bands of the donor (600 nm) and an electron acceptor (335 and 450 nm) for the RC in the water-glycerol and trehalose environment. Before measurements the preparations were frozen to -180°C in the dark and under activating light, then in the heating process the T-dependence of the recombination rate was measured. In similar conditions the fluorescence lifetime of tryptophanils (reg=315 and 345 nm) were registered. It was established that the recombination rate constant in the RC preparations dissolved in water-glycerol medium and frozen in the dark when measured at 600 and 450 nm is equal. On the other hand in the RC with the isotopic substitution of H2O for D2O the recombination kinetics in the band of 450 nm was slower than that in the 600 nm band. In preparations frozen in the light of this difference we did not observe. A correlation was found between the temperature dependence of the recombination rate and lifetime of the tryptophanil fluorescence in RC protein complexes in different solvents. Additionally differences in the average lifetime (τm) of tryptophanils fluorescence in RC preparations frozen in the dark or under activating light were measured. These results are explained due to RC transitions between different conformational states as well as by processes of proton relaxation in the structure of the hydrogen bonds in the environment of RC cofactors.