Light-Induced Charge Separation in Photosynthetic Bacterial Reaction Centers Monitored by FTIR Difference Spectroscopy: the QA Vibrations

The crystal structure of the photosynthetic bacterial reaction center (RC) suggests that the localization and the conformation of the cofactors involved in the electron transport is optimized by the protein environment which would then be responsible, at least in part, for the efficiency and quasi-irreversibility of the charge separation. For example, the difference in the nature and organization of the amino acids lining the binding pocket of the primary (QA) and secondary (QB) quinones, which are both a ubiquinone (UQ10) in Rb. sphaeroides, might explain the differences in the redox properties of the two quinones as well as their very distinct roles in the electron transfer and proton transport mechanisms. However, X-ray studies yield an essentially static picture of the RC in the neutral state and do not provide information on the light-induced structural changes accompanying the charge separation and stabilization processes.