The molecular events leading to photosynthetic water oxidation are still largely unknown, particularly the proteins involved and the specific residues that form ligands to manganese, an essential cofactor for oxygen evolution. Current models suggest the participation of the reaction center D1D2 complex and an extrinsic 33kD protein, called the manganese stabilizing protein. This research will combine the techniques of site-directed mutagenesis, using the readily transformable cyanobacterium Synechocystis 6803, to modify selected amino acid residues comprising the so-called manganese stabilizing polypeptide, together with EPR and ENDOR spectroscopic methods which enable a direct assessment of these changes on the structure and kinetic properties of the manganese site and other endogenous electron donors coupled to the reaction center, such as Cytb559 and Tyr- 160.%%% Photosynthesis is the most pervasive biological reaction on the face of the earth. It produces nearly all of the oxygen in the air which is essential for oxidative metabolism in all aerobic organisms and for combustion in fossil fuel powered engines. Thus, photosynthetic O2 evolution powers most biological and commercial machines. Presently there are no man-made catalysts capable of carrying out the efficient evolution of O2 from water and an energy source with a commercially useful yield. Nature, on the other hand, has developed a unique enzyme, found in all O2-evolving plants and algae, optimized for catalyzing this process. This research will contribute to the understanding of the molecular basis by which green plants are capable of harnessing nature's most power oxidant, the splitting of the water by a manganese-containing enzyme. By understanding this biological process we hope to gain insight that will lead to a new blueprint for the design of synthetic water oxidizing catalysts.*** //
