9727607 Blankenship The objective of this research is to extend the current understanding of the energy trapping processes, primary photochemistry and early secondary electron transfer reactions in photosynthetic reaction centers that contain FeS centers as early electron acceptors. The particular systems that will be studied include reaction centers from the primitive anoxygenic organisms known as heliobacteria as well as Photosystem I of oxygenic photosynthetic organisms. One of the overall goals of the work is to correlate some of the pigments observed in spectroscopic studies with pigments observed in the recent X-ray structure of Photosystem I. Specific proposed experiments include, picosecond transient absorbance measurements in the blue spectral region in Photosystem I, studies on Photosystem I mutants in the quinone-binding region and the P700 binding region, dichroism experiments on Photosystem I and investigation of secondary electron transfer reactions in heliobacteria monitored using EPR and picosecond timescale transient absorbance spectroscopy. These experiments will give new insights into the energy trapping process in reaction centers that contain integral core antenna pigments and will help to identify and characterize some of the early electron acceptors in these systems, including chlorophylls, quinones and FeS centers. The goal of this work is to understand how plants and other photosynthetic organisms convert the energy of sunlight into chemical energy. This project is designed to give detailed knowledge of the chemical mechanism of energy storage in a class of photosynthetic complexes that is not well understood. Advances in understanding the basic scientific principles at work in this essential biological process may ultimately lead to the development of artificial energy storage systems. The artificial systems may decrease our dependence on fossil fuels and reduce emission of pullutants and greenhouse gases. Another possible benefit is the use of this knowledg e in the development of improved plants that will help meet our food and fiber needs. ***
