Two stable electron-conformational states of photoactivated reaction center and their observation in primary donor recovery kinetics

We investigated the peculiarity of primary donor recovery kinetics in the reaction centers from the purple bacteriaRb. Sphaeroides at low levels of their cw photoactivation. A pronounced biphasity of the relaxation kinetics was found for the total light activating intensity <5×10¹² quanta·cm^-2·s^-1. The effect was attributed to strong dependence of an electron transfer rate constant for the reactionP ⁺Q _infA ^pup- Q_B P ⁺Q_AQ _infB ^sup- upon the RC conformational state controlled by the light. We showed the existence of two different electron-conformational states for the photoexcited RC. The first reveals itself at low intensity of cw photoactivation while the second becomes actual under the intensity >5×10¹² quanta · cm^-2 · s^-1.