The spectral-kinetic indicators of relaxation processes following the electron stabilization into the acceptor compartment of photosynthetic RCs of bacteria.

Abstract

Longterm temporary stabilization of the electron in the acceptor part of the photosynthetic reaction center (RC) is essential for subsequent efficient trans� fer of reducing equivalents to the photosynthetic membrane. Comparative study of the kinetics of redox reactions of photoactive bacteriochlorophyll of the RC of purple bacteria and quinone acceptors in their indi� vidual absorption bands is an informative approach to study the mechanisms of this stabilization. The analy� sis of the revealed kinetic differences makes it possible to estimate the activation energy and the characteristic time of the transition relaxation process associated with the stabilization of the electron on the final quinone acceptor and establish the hydrogen bonds in the quinone environment that are involved in this pro� cess. Conformational dynamics of protein-pigment complexes of photosynthetic RCs plays the crucial role in all stages of light energy conversion, including the temporary stabilization of electrons in the quinone acceptor component of the RCs of purple bacteria (1, 2). The important functional role of effective oper� ation of this component of the electron transport chain (ETC) is determined primarily by the fact that it couples the very fast initial stages of the lightinduced charge separation with the significantly slower diffu� sioncontrolled reactions of transferring the reducing equivalents to the membrane. Ultimately, two quinone molecules, QA and QB, integrated into the RC struc� ture, are actively involved in the coupled electron- proton transport processes that lead to the formation of a proton gradient across the photosynthetic mem� brane, required for the synthesis of ATP. These two quinones have different redox potentials, providing the driving force for the vector electron transfer from the primary to the secondary quinone acceptor. Since