Probing light-induced conformational transitions in bacterial photosynthetic reaction centers embedded in trehalose-water amorphous matrices.

Abstract The coupling between electron transfer and protein dynamics has been studied in photosynthetic reaction centers (RC) from Rhodobacter sphaeroides by embedding the protein into room temperature solid trehalose–water matrices. Electron transfer kinetics from the primary quinone acceptor (Q A − ) to the photoxidized donor (P + ) were measured as a function of the duration of photoexcitation from 20 ns (laser flash) to more than 1 min. Decreasing the water content of the matrix down to ≈5×10 3 water molecules per RC causes a reversible four-times acceleration of P + Q A − recombination after the laser pulse. By comparing the broadly distributed kinetics observed under these conditions …