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Content archived on 2024-04-30

The catalytic site of photosynthetic oxygen evolution studied by electron paramagnetic resonance and optical spectroscopy in photosystem ii core particles


Research objectives and content The mechanism of photosynthetic water oxidation at the oxygen evolving complex of Photosystem II (PSII) of green plants and cyanobacteria is one of the major enigmas of molecular bioenergetics. The roles of the cofactors (manganese, amino acids, calcium, chloride) are unclear. The current research has been widely based on magnetic resonance and optical spectroscopy, but these methods have rarely been combined. The present project aims at a combination of these approaches to resolve several apparent contradictions which have arisen from the use of these methods in isolation and to extend the spectroscopic studies in order to resolve fundamental questions of the enzyme mechanism. A biochemical PSII preparation suitable for both methods will be developed based on preparations of detergent-solubilised protein complexes, so called PSII cores. Enzymological manipulations (calcium-depletion, a range of chloride-depletion methods and anion replacements, NH3- and NO-binding, and combinations of these treatments) will be applied to PSII cores and these will be characterized by both EPR and optical methods. By comparison of the planned EPR/optical study with earlier EPR work from mainly the Saclay group and recent optical data from the Osnabr|ck group, it is expected that an improved model for the energetics and mechanism of water oxidation by Photosystem II will develop. Training content (objective, benefit and expected impact) The group of A.W. Rutherford at Saclay is one of the most experienced groups in the application of EPR spectroscopy to Photosystem II. In Osnabr|ck I have been working mainly with optical spectroscopy. At Saclay I will learn the techniques of magnetic resonance spectroscopy. By integrating the state-of-the-art knowledge and techniques from biochemistry, EPR-, and optical spectroscopy I will try to reconcile recent, apparently contradicting results in the field of research on Photosystem II. Links with industry / industrial relevance (22)

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Ctr Etudes de Saclay - CE-S 532

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