The role of structural-dynamic organization of the reaction centers of purple bacteria Rhodobacter sphaeroides in the picosecond stages of photoinduced reactions

摘要

The temperature dependences of the rates of excitation energy migration from BPh-M to photoactive BChl (P), charge separation and electron transfer to the primary quinone Q_A were investigated in the reaction centers (RC) from Rb. sphaeroides. A native RC and that modified by adding 40% of dimetilsulphoxide (DMSO) were used. Modification of the RC by DMSO decreases both the energy migration process and the rates of electron transfer. As temperature decreases from 300 to 77 K, the energy migration rate drops by a factor of 1.8 for the control sample and by 3.2 for th.e modified RC. The rate of charge separation increases under these conditions in control and under modification by factors 2.2 and 2, accordingly. The rate of electron transfer from I to Q_A increases under cooling by a factor of 3 for the native RC and by a factor of 2 for the modified preparations. The results were discussed in the framework of the presence of fast relaxation processes (including polarization of molecules surrounding pigment cofactors) in the initial stages of photosynthesis. It was concluded that light H-containing molecular groups in the RC structure are capable to effectively accept a part of the energy dissipated at initial stages.