Journal
BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS
Volume 1655, Issue 1-3, Pages 158-171Publisher
ELSEVIER
DOI: 10.1016/j.bbabio.2003.11.009
Keywords
ENDOR; ESEEM; multiline EPR signal; S-0-state substrate water binding
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Funding
- NIGMS NIH HHS [GM48242] Funding Source: Medline
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The pulsed electron paramagnetic resonance (EPR) methods of electron spin echo envelope modulation (ESEEM) and electron spill echo-electron nuclear double resonance (ESE-ENDOR) are used to investigate the structure of the Photosystem II oxygen-evolving complex (OEC), including the paramagnetic manganese cluster and its immediate surroundings. Recent unpublished results from the pulsed EPR laboratory at UC-Davis are discussed, along with aspects of recent publications, with a focus on substrate and cofactor interactions. New data on the proximity of exchangeable deuterons around the Mn cluster poised in the So-state are presented and interpreted. These pulsed EPR results are used in an evaluation of several recently proposed mechanisms for PSII water oxidation. We strongly favor mechanistic models where the substrate waters bind within the OEC early in the S-state cycle. Models in which the O-O bond is formed by a nucleophilic attack by a Ca2+-bound water on a strong S-4-state electrophile provide a good match to the pulsed EPR data. (C) 2004 Elsevier B.V. All rights reserved.
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