ИСТИНА

Long time stabilisation of electron in the photosynthetic reaction centre (RC) acceptor part has essential value for effective carrying over of reducing equivalents to a photosynthetic membrane. For studying of mechanisms of this stabilisation informative there is a comparative investigation of kinetics of redox transformations for photoactive bacteriochlorophyll (P) of purple bacteria RC and quinone acceptors (QA and QB) in their individual absorption bands. The revealed difference in the kinetics of dark recombination of charges photoseparated between P and QB, recorded in the P absorption band (600 nm) and the absorption bands of RC ubiquinones (335 nm, 450 nm) in RCs of Rb. sphaeroides is apparently due to some polarization and structural changes in the QB environment, leading to a “lag” in the return of QB absorption to the original dark level as compared to the changes in dimer P band. The substitution Н2О with D2O not only slowed down the rate of back electron transfer from QB- but also increased the observed difference in the kinetic curves recorded at 600 and 450 nm. These differences disappeared with the addition of 10% (v/v) DMSO to RC preparations (DMSO - strong proton–acceptor agent penetrating the RC structure, modifies the network of hydrogen bonds in RC). Such differences did not register for dark recombination kinetics between Р + and QA - in control samples of RCs. The differences, however, were shown after isotope substitution and they increased in process of cooling of the RC samples to cryogenic temperatures in the dark. But the differences are not found out for the RC samples cooled on exciting light. It is possible to state the certain conclusions about the hydrogen bonds involved in processes of electrostatic stabilization of electron in the quinone environment in the RC structure.