Biopolymers and cell. 2002; 18 (3): 196 - 204

Slow conformational dynamics of the reaction centers from Rhodobacter sphaeroides under photoactivation at different temperatures

M. T. Kapustina, Yu. M. Barabash, A. O. Gouskcha, M. V. Olencfiuk, V. N. Kharkyanen

We experimentally investigated kinetics of the reaction centers (RCs) optical absorbance at the different exposition times (from 0.1 s to 400 s) of actinic light at two temperatures (Tl -3 °C and T2 - 22 °C). At short photoexcitation times (less 1 s) the optical absorbance kinetics under illumination and after turning it off was the same in both cold and warm samples. It is interesting that in the cold samples at the photoexcitation times 2 s—50 s the RCs possessing the slow recombination component have no time to be accumulated, and we observed a recombination kinetics faster than that in warm samples. However, with this time sufficiently long (> 300 s), the situation changes to opposite and the recombination kinetics of the cold samples becomes slower than that of the warm one. To describe qualitatively all the manifold of data obtained we used the general basic fokker-Planck-type equations for a two-level system. In our model we took into consideration the temperature dependence of two parameters: the system diffusion along structure potential and the rate of electron transfer between quinone acceptors. The results of the computer modeling of absorbance changes at different temperatures are in good agreement with the experimental data.