9604339 Bricker Part 1-Technical This research will further elucidate the structural organization of proteins within Photosystem II. Protein-protein and protein-cofactor interactions among the components of the photosytem will be studied using a combination of biochemical and molecular tools. First, the site-specific protein-labeling reagents NHS-biotin will be used o probe interacting domains on the extrinsic proteins of the photosystem. Labeling will be performed on a number of biochemically resolved Photosystem II complexes and on the extrinsic proteins free in solution The modified domains on the 33 kDa, 24 and 17 kDa extrinsic proteins will be identified by a combination of affinity purification, protease digestion and matrix-assisted laser desorption/ionization mass spectrometry. Second, suppressor analysis will be performed on spontaneous and chemically induced revertants of the CP 7 mutants W167S and RR384385EE. Intergenic suppressors will be identified, mapped and sequenced to determine the identity of proteins interacting with these location in the CP 47 protein. Third, protein footprinting using the non-specific chemical protease Fe-EDTA will be used to map interactions within the photosystem. Photosystem II complexes in various states of biochemical resolution will be subjected to chemical protease treatment. Protected domains on a number of Photosystem II components (CP 47, D1 and the 33 kDa extrinsic protein) will be identified by "Western blotting" and probing with N-and C-terminal specific antibody reagents. These experiments should provide relatively high resolution information concerning interacting domains on these protein components. Part 2-Non Technical Elucidation of the functional properties and structural organization of membrane protein complexes is one of the central objectives of current biochemical investigation. Biological membranes are involved in virtually every aspect of cellular organization and activity. One of the most intriguing aspects of membrane function is its role in the mediation of energy transduction in photosynthetic organisms. Light energy, which is the product of a most violent physical process, fusion, is transformed into biological energy equivalents utilized by the photosynthetic cell. The photosynthetic process provides both the carbohydrate which lies at the base of virtually all food chains and, as a byproduct, all of the atmospheric oxygen utilized by higher organisms. This project investigates the structural interactions between the proteins involved in oxygen evolution. An understanding of the structure of the oxygen evolving complex will yield new insights into the how this important membrane protein complex functions.