Energetics of the S2 State Spin Isomers of the Oxygen-Evolving Complex of Photosystem II
© 2017 American Chemical Society. 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 S2QA- decay under light-limiting conditions.
Publication Source (Journal or Book title)
Journal of Physical Chemistry B
Vinyard, D., Khan, S., Askerka, M., Batista, V., & Brudvig, G. (2017). Energetics of the S2 State Spin Isomers of the Oxygen-Evolving Complex of Photosystem II. Journal of Physical Chemistry B, 121 (5), 1020-1025. https://doi.org/10.1021/acs.jpcb.7b00110