[On the mechanism for stabilizing a long-living charge separated state of photosynthetic reaction centers frozen under intensive illumination].

ABSTRACT

It is shown that freezing of the photosynthetic reaction centers from purple bacteria Rhodobacter sphaeroides under intensive illumination leads to the appearance of long-living charge separated states of reaction centers (P(+)QA-). This implies that the recombination reactions is blocked or charge separated state is stabilized. Experimental data are presented. It is also shown that this stabilization effect is caused by the structural relaxation of reaction centers to a new equilibrium state, and the free energy difference decreases as a result of this relaxation. The possible mechanism of such relaxation is determined by the effect of the polar water molecules orientation in the semiquinone local electrostatic field. The detailed analysis of the stabilization effect has been carried out, and its result supports a hypothesis of non equilibrium state of many electron transfer reactions in biological systems.