title: Energetics of the S2State Spin Isomers of the Oxygen-Evolving Complex of Photosystem II.
abstract: The S2redox intermediate of the oxygen-evolving complex in photosystem II is present as two spin isomers. The S = 1/2 isomer gives rise to a multiline electron paramagnetic resonance (EPR) signal at g = 2.0, whereas the S = 5/2 isomer exhibits a broad EPR signal at g = 4.1. The electronic structures of these isomers are known, but their role in the catalytic cycle of water oxidation remains unclear. We show that formation of the S = 1/2 state from the S = 5/2 state is exergonic at temperatures above 160 K. However, the S = 1/2 isomer decays to S1more slowly than the S = 5/2 isomer. These differences support the hypotheses that the S3state is formed via the S2state S = 5/2 isomer and that the stabilized S2state S = 1/2 isomer plays a role in minimizing S2QA-decay under light-limiting conditions.
authors.affiliation: Department of Chemistry, Yale University , New Haven, Connecticut 06520-8107, United States.
authors.forename: David J
authors.initials: DJ
authors.lastname: Vinyard
authors.affiliation: Department of Chemistry, Yale University , New Haven, Connecticut 06520-8107, United States.
authors.forename: Sahr
authors.initials: S
authors.lastname: Khan
authors.affiliation: Department of Chemistry, Yale University , New Haven, Connecticut 06520-8107, United States.
authors.forename: Mikhail
authors.initials: M
authors.lastname: Askerka
authors.affiliation: Department of Chemistry, Yale University , New Haven, Connecticut 06520-8107, United States.
authors.forename: Victor S
authors.identifier: 0000-0002-3262-1237
authors.initials: VS
authors.lastname: Batista
authors.affiliation: Department of Chemistry, Yale University , New Haven, Connecticut 06520-8107, United States.
authors.forename: Gary W
authors.identifier: 0000-0002-7040-1892
authors.initials: GW
authors.lastname: Brudvig
mesh_terms: D007536:Isomerism; D007700:Kinetics; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000378:metabolism*; D011789:Quantum Theory; D018724:Spinacia oleracea / Q000201:enzymology; D014867:Water / Q000737:chemistry
chemical_list: D045332:Photosystem II Protein Complex; D014867:Water; D010100:Oxygen