Primary Electron Transfer Reactions in Membrane-Bound Open and Closed Reaction Centers from Purple Bacterium Rhodobacter sphaeroides

Abstract

Most ultrafast transient absorption studies of primary electron transfer in reaction centers from purple bacteria have been performed in complexes isolated from their natural lipid membrane environment using detergent. In this contribution we present near-UV-vis transient absorption studies of reaction centers embedded in their natural membrane environment. The evolution of absorption spectra recorded with subpicosecond resolution and re ecting primarily electron transfer reactions has been compared to data obtained previously for isolated reaction centers. We conclude that the overall spectral evolution in both types of samples is similar, and the environment of the reaction center protein has only a minor e ect on the primary electron transfer reactions. The di erences between the two samples are explained in terms of di erent energetic levels (and their di erent temporal evolution) of the two initial charge separated states PBA and P HA , with P being the primary electron donor and BA and HA the two consecutive electron acceptors. Additionally, in the electric eld generated by P HA , BA in membrane-bound reaction centers undergoes a stronger electrochromic shift than in isolated reaction centers.