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Challenges in Enzyme Catalysis - Photosystem II and Orotidine Decarboxylase : A Density Functional Theory Treatment

<p>Possibly the most fascinating biochemical mechanism remaining to be solved is the formation of oxygen from water in photosystem II. This is a critical part of the photosynthetic reaction that makes solar energy accessible to living organisms.</p><p>The present thesis uses quantum chemistry, more specifically the density functional B3LYP, to investigate a mechanism where an oxyl radical bound to manganese is the active species in O-O bond formation. Benchmark calculations on manganese systems confirm that B3LYP can be expected to give accurate results. The effect of the self-interaction error is shown to be limited. Studies of synthetic manganese complexes support the idea of a radical mechanism. A manganese complex with an oxyl radical is active in oxygen formation while manganese-oxo complexes remain inactive. Formation of the O-O bond requires a spin transition but there should be no effect on the rate. Spin transitions are also required in many short-range electron-transfer reactions.</p><p>Investigations of the superproficient enzyme orotidine decarboxylase support a mechanism that involves an invariant network of charged amino acids, acting together with at least two mobile water molecules.</p>

Identiferoai:union.ndltd.org:UPSALLA/oai:DiVA.org:su-486
Date January 2005
CreatorsLundberg, Marcus
PublisherStockholm University, Department of Physics, Stockholm : Fysikum
Source SetsDiVA Archive at Upsalla University
LanguageEnglish
Detected LanguageEnglish
TypeDoctoral thesis, comprehensive summary, text

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