NSF Award
9017526
This research is designed to determine how the structure of photosystem II (PSII) and associated cofactors mediate electron transfer from water to the primary electron donor, P680. The focus of this project is on the role of the D1 reaction center polypetide of PSII in oxygen evolution. Mutant strains of Chlamydomonas which still accumulate PSII reaction center complexes but which show impaired electron transfer, particularly on the oxidizing side of the complex are being identified and isolated by Dr. Jeanne Erickson at UCLA. These mutants are being characterized biophysically and compared to wild-type cells by examining: 1) the concentration of PSII reaction centers, 2) the relative rates of electron transfer and the equilibrium constants which govern electron transfer between the OEC, Z and the oxidized primary electron, P680+, 3) the quantum yield of primary charge separation, 4) the amount of oxygen released in each of a series of saturating light flashes and 5) the number of oxidizing equivalents that can be extracted from the donor side before electron transfer is halted. Altered optical and EPR spectroscopic signals arising from the oxidizing side of the reaction center as well as the concentration of the manganese cluster associated with PSII responsible for the oxidation of water to molecular oxygen are being studied in collaboration with Dr. Gary Brudvig of Yale University. Terrestrial, aquatic and marine plants are the primary source of renewable biomass on earth. Through the process of photosynthesis plants convert radiant energy received from the sun into chemical energy. This energy drives the conversion of atmospheric carbon dioxide into sugars and other compounds, such as fats and proteins, which are essential components of all living organisms. Photosynthesis also results in the production of oxygen, and this oxygen is crucial for sustaining all forms of life that rely on respiration in order to provide the energy to keep them alive. The purpose of this research project is to gain an increased understanding of the biochemical and physical reactions that take place during photosynthesis by plants, resulting in the production of oxygen and consumption of carbon dioxide. Most of this research will be done on a simple unicellular plant which is well suited to analysis by modern molecular biology and therefore provides an excellent model system for study.
