Mechanism and Macromolecular Organization in Photosynthetic Reaction Centers and Membranes

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This proposal requests continued support for biophysical studies of the mechanism of the charge separation and recombination steps in photosynthetic reaction centers (RCs) and the higher-order organization of photosynthetic membranes. An important part of our work involves the development of new experimental and theoretical methods that can have a broad impact in other areas of science and biotechnology. Understanding the mechanisms of energy and electron transfer in photosynthetic systems has proven to be an exceptionally fertile area for such developments and for training scientists. In this project, research will be performed in the following specific areas that relate to the mechanism of charge separation in the reaction center: (i) determination of the fundamental parameters that control alternative electron transfer pathways initiated by excitation of the monomeric bacteriochlorophyll on the functional side using resonance Stark spectroscopy; (ii) application of the resonance Stark method to other pathways created by engineering the RC; (iii) measurements of the activation energy and magnetic field dependence of the decay of the special pair triplet state to determine the energetics of the primary charge separation in RC mutants; (iv) attachment of spectator dye molecules near the functional components to probe the dynamics of charge motion during the first electron transfer step(s); (v) organization of components in the photosynthetic membrane in supported bilayers. By integrating this range of approaches, our understanding of the mechanism of initial electron transfer and the related phenomenon of unidirectional electron transfer can be advanced and brought into the larger context of structure-function relationships in complex biological assemblies.