Energetics of the S2 State Spin Isomers of the Oxygen-Evolving Complex of Photosystem II

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• 作者：David J. Vinyard ; Sahr Khan ; Mikhail Askerka ; Victor S. BatistaGary W. Brudvig
• 刊名：Journal of Physical Chemistry B
• 出版年：2017
• 出版时间：February 9, 2017
• 年：2017
• 卷：121
• 期：5
• 页码：1020-1025
• 全文大小：440K
• ISSN：1520-5207

文摘

The S₂ redox 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 S₁ more slowly than the S = 5/2 isomer. These differences support the hypotheses that the S₃ state is formed via the S₂ state S = 5/2 isomer and that the stabilized S₂ state S = 1/2 isomer plays a role in minimizing S₂Q_A^– decay under light-limiting conditions.