RUI: The Use of Anion Inhibitors to Investigate the Role of Chloride in Oxygen Evolution by Photosystem II of Higher Plants

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The importance of chloride for the formation of molecular oxygen by higher plants will be investigated in this project. Oxygen, which is required by all respiring life forms, is evolved as a byproduct of the conversion of light energy into chemical energy during photosynthesis. The production of oxygen is therefore among the most important biochemical reactions for the support of life on earth. Oxygen is formed by the oxidation of water at a cluster of manganese ions in Photosystem II, a membrane-bound protein complex. Chloride is required as a cofactor for this catalysis. The approach to be taken in this project will be to characterize the action of anions that inhibit oxygen evolution activity by competing with functional chloride. Inhibitor studies are valuable in pointing out the characteristics of normal function. Using photosystem II-enriched membranes from spinach, the effects of anion inhibitors such as F-, N3-, I-, NO2-, and NO3- on the enzyme kinetics of oxygen evolution activity will be analyzed. These results will be compared with the effects of the anions on the electron paramagnetic resonance (EPR) spectra of the manganese cluster and other redox active centers. Studies will also be undertaken to characterize some of the anions as activators of oxygen evolution along with chloride itself and bromide. These experiments will facilitate the interpretation of the effects of the anion inhibitors at a molecular level. Since this project will be carried out at a primarily undergraduate university, this project will provide beginning researchers with laboratory experience, which is expected to influence their career choices.