Infrared Spectroscopic Investigation of the QA Site of Photosynthetic Reaction Centers by Replacing the Native Quinone with Structurally Different Analogs

The bacterial photosynthetic reaction center (RC) of Rhodobacter (Rb.) sphaeroides performs light-induced charge separation by transferring an electron from a donor P (a bacteriochlorophyll a-dimer) to the acceptors QA and QB (quinones). With X-ray analysis of RC crystals [1] it has been possible to obtain information on the level of individual bonds. Since only the ‘resting’ state of the protein is observed, and atom positions should be considered as average values, other methods are necessary to study the small changes the RC undergoes upon charge-separation.