Pressure effects on the photochemistry of bacterial photosynthetic reaction centers from Rhodobacter sphaeroides R-26 and Rhodopseudomonas viridis

Abstract

Electron-transfer reactions and triplet decay rates have been studied at pressures up to 300 MPa. In reaction centers from Rhodobacter sphaeroides R-26, high pressure hastened the electron transfers from both the primary and secondary quinones (Q A and Q B) to the primary electron donor bacteriochlorophyll, P. Motion of Q A between two sites, one nearer to P and the other nearer to Q B, could account for these pressure effects. In reaction centers from Rhodopseudomonas viridis, charge recombination was slowed by high pressure. Decay rates were also studied for the triplet state, P R. In Rb. sphaeroides R-26 with Q A reduced with Na 2S 2O 4, the decay was hastened by pressure. This could be explained if P R decays through a charge-transfer triplet state, or if the decay kinetics of P R are sensitive to the distance between P and Q A −. In Rps. viridis reaction centers, and in Rb. sphaeroides reaction centers that were depleted of Q A, the lifetime of P R was not altered by pressure.