Primary Processes in Photosystem I

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Photosynthetic organisms use a twofold strategy to capture and store solar energy. An antenna system first collects light and then transfers the energy to an electron transfer system that converts electronic excitation into redox energy that can be used for cell growth. In most photosynthetic systems, the antenna and electron transfer functions are located on separable complexes and can be studied independently. However, in Photosystem I of oxygenic photosynthetic organisms, the antenna and electron transfer functions are fused into a single large complex that serves both functions. Experiments are proposed to improve our current fragmentary understanding of the energy trapping processes, primary photochemistry and early secondary electron transfer reactions in this important class of photosynthetic reaction centers. Overall goals of the work are to understand the coupling of the antenna system to the electron transfer system and the pathway of the early electron transfer processes. Specific experiments in this project include: 1) Studies on Photosystem I mutants in the quinone and pigment binding regions, 2) Separation of the Photosystem I reaction center complex into antenna and electron transfer domains using protein engineering and 3) Analysis of Photosystem I energy trapping and electron transfer in a newly-discovered chlorophyll d-containing organism, Acaryochloris marina. This project will increase our understanding of how plants and other photosynthetic organisms convert the energy of sunlight into chemical energy. The process of photosynthesis supplies all of our food and most of our energy needs. This project is designed to give detailed knowledge of the chemical mechanism of this essential biological process.