Biggins 9404744 The research is an investigation with two related objectives on the structure and function of the photosynthetic reaction center, Photosystem 1. 1) The first objective is a continuation of studies on the mechanism ofinteraction of the core heterodimer, which bears the cofactors for charge separation and early electron transfer acceptors, with a small subunit PsaC which carries the terminal iron sulfur centers. This will be accomplished by creating site directed mutations in the putative binding domain of the PsaC subunit in the core heterodimer and on the PsaC subunit itself. Electron transfer reactions will be followed to determine the success of the reconstitutions of the heterodimer using PsaC, PsaD and cluster insertion protocols in vitro. 2) The second objective is a continuation of investigations concerning the function of phylloquinone as a transient acceptor on the core heterodimer. The role of the secondary quinone in Photosystem 1 remains elusive, and we propose experiments to determine its possible function in the primary photochemistry of the reaction center. We have shown that the binding site of the primary quinone involved in forward electron transfer can be inhibited. We will investigate the inhibition in more detail to study properties of the quinone binding site and select new inhibitors. Basic research in this area is important because of the potential for developing herbicides selective for Photosystem 1. The third objective on protein design proposed in the original request will not be pursued because of a lack of sufficient funds in the award. %%% This research to be continued under the auspices of the National Science Foundation concerns the mechanism of photosynthesis. Photosynthesis is a fundamental process in plant biology whereby solar energy is used to provide the driving force for the uptake of carbon dioxide from the atmosphere and its conversion into all the different products needed for the plant. This is the only form of biosolar conversion and animal life depends upon this process for the production of all food. We also rely on this process for the generation of forest products for construction, paper, packaging and countless other materials. The origin of all fossil fuels such as oil, gas and coal now presently being expended was via a photosynthetic conversion of solar energy by prehistoric plants. The process of photosynthesis in plants occurs in biological membranes in the leaf tissue and it is possible to isolate the solar conversion enzyme systems called reaction centers in the laboratory. Progress is now being made on details of the atomic structure of these reaction centers and their chemical function. The specific work in this project focuses on structure-function aspects using biochemical techniques to dissociate the reaction centers into the individual proteins and molecules actively involved in the solar conversion process so they can be identified and characterized. Molecular genetic methods are used to make alterations in these proteins to provide information on their function. The justification of research in photosynthesis is that when a complete understanding of the mechanism of reaction center function has been elucidated it will lead to: increased yields of food and biomass for fiber, construction materials andliquid fuels such as ethyl alcohol which is presently being used in mixtures with gasoline for cleaner automobile use. the engineering of devices that would be competitive with photovoltaic cell for the direct conversion of sunlight into electricity. the photo-production of hydrogen as a fuel. the design of selective herbicides for the control of crops and fores productivity.
