Primary Electron Transfer Processes in Photosynthetic Bacterial Reaction Centers

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Issues which are key to obtaining a fundamental understanding of the charge separation process in bacterial photosynthetic reaction centers (RCs) will be investigated using time-resolved absorption spectroscopy of wild-type RCs, RCs having site- directed mutations and RCs chemically modified to remove or alter a specific cofactor. Dr. Holten plans to study unresolved issues on the details of the involvement of the RC prosthetic groups in electron transfer and open up new frontiers on the role of the protein, both static and dynamic, in the charge separation process. The reaction center is the photochemical heart of a photosynthetic organism. The function of this membrane-bound pigment-protein complex is to transform light energy into chemical energy. Understanding how the RC carries out its unique role in photosynthesis has been the subject of intense effort since the RC from the bacterium Rb. sphaeroides was isolated about 20 years ago. Recently the ability to investigate and understand the internal properties and operation of the bacterial RC took a quantum leap forward as a result of the solution of the three-dimensional structure of the RC complex from Rps. viridis. Spectroscopic studies of the RC primary photochemistry have thus been refocused to a more detailed and fundamental level and at the same time have taken on a much broader significance than ever before. The studies planned will yield diverse information that is critical not only for elucidating the molecular mechanisms by which the RC functions, but, also, will advance knowledge in the areas of electron transfer, pigment-protein interactions and protein dynamics.