Protein dynamics control of electron transfer in photosynthetic reaction centers from Rps. sulfoviridis.

In the cycle of photosynthetic reaction centers, the initially oxidized special pair of bacteriochlorophyll molecules is subsequently reduced by an electron transferred over a chain of four hemes of the complex. Here, we examine the kinetics of electron transfer between the proximal heme c-559 of the chain and the oxidized special pair in the reaction center from Rps. sulfoviridis in the range of temperatures from 294 to 40 K. The experimental data were obtained for three redox states of the reaction center, in which one, two, or three nearest hemes of the chain are reduced prior to special pair oxidation. The experimental kinetic data are analyzed in terms of a Sumi-Marcus-type model developed in our previous paper,1 in which similar measurements were reported on the reaction centers from Rps. viridis. The model allows us to establish a connection between the observed nonexponential electron-transfer kinetics and the local structural relaxation dynamics of the reaction center protein on the microsecond time scale. The activation energy for relaxation dynamics of the protein medium has been found to be around 0.1 eV for all three redox states, which is in contrast to a value around 0.4-0.6 eV in Rps. viridis.1 The possible nature of the difference between the reaction centers from Rps. viridis and Rps. sulfoviridis, which are believed to be very similar, is discussed. The role of the protein glass transition at low temperatures and that of internal water molecules in the process are analyzed.

[A rapid method to evaluate potential vasodilatory activity of organic nitrates].

The kinetics of interaction between organic nitrates (3,3-bis(nitroxymethyl)oxetane) and cysteine were evaluated by the rate of nitrite ion formation at various concentrations of reagents and pH. The activities of natural reducing agents, including cysteine, glutathione, and NADH, in generating the nitrite ion from organic nitrates (3,3-bis(nitroxymethyl)oxetane) were compared. Cysteine was shown to be the most potent reducing agent. Studying the effectiveness of nitrates (trinitroglycerol, 3,3-bis(nitroxymethyl)oxetane, and nicorandil) at a concentration of 3 mM showed that the rate of nitrite ion accumulation in the reaction with 10 mM cysteine is 1.66, 0.37, and 0.02 microM/min, respectively.

Effect of protein relaxation on electron transfer from the cytochrome subunit to the bacteriochlorophyll dimer in Rps. sulfoviridis reaction centers within mixed adiabatic/nonadiabatic model.

The broad set of nonexponential electron transfer (ET) kinetics in reaction centers (RC) from Rhodopseudomonas sulfoviridis in temperature range 297-40 K are described within a mixed adiabatic/nonadiabatic model. The key point of the model is the combination of Sumi-Marcus and Rips-Jortner approaches which can be represented by the separate contributions of temperature-independent vibrational (v) and temperature-dependent diffusive (d) coordinates to the preexponential factor, to the free energy of reaction DeltaG=DeltaG(v)+DeltaG(d)(T) and to the reorganization energy lambda=lambda(v)+lambda(d)(T). The broad distribution of protein dielectric relaxation times along the diffusive coordinate is considered within the Davidson-Cole formalism.

[Effect of molecular dynamics on the photoinduced electron transfer in eosin-myoglobin complex]. / Vliianie molekuliarnoi dinamiki na fotoindutsirovannyi perenos électrona v komplekse éosin-mioglobin.

The temperature dependence of the rate constant of photoinduced electron transfer in the modified eosin-myoglobin complex by monitoring of the phosphorescence quenching of eosin is measured. The values of electron transfer rate constants are equal 10(2) + 10(3) s-1 in the temperature region 150-200 K. The kinetics of relaxation of the maximum of the time-resolved phosphorescence spectra of eosin on apomyoglobin is measured in the same temperature range. The solvation relaxation of the time-resolved phosphorescence spectra is nonexponential. The characteristic times of the solvation relaxation are given 10(-2) + 10(-4) s-1, that correlate with the time of electron transfer in this system. It was observed the "acceleration" of the relaxation rate of the time-resolved phosphorescence spectra of eosin in metmyoglobin due to nonequilibrium photoinduced electron transfer. The role of the matrix dynamics in photoinduced electron transfer in proteins is discussed.