EPR/ENDOR Studies of Plastoquinone Anion Radical in Photosystem II (QA-̣ and in Organic Solvents
The electron acceptors QA and QB in Photosystem II are known to be two specially bound plastoquinone molecules assumed to be linked by a histidine-liganded Fe2+ ion whose function is unknown. EPR/ENDOR spectroscopy (1) can, in principle, be applied to the quinone radical anions formed in the charge separation process, in order to gain information about their electronic structure. Due to the strong magnetic coupling between the semiquinones and the high spin Fe2+, ENDOR spectra are difficult to obtain. The removal of Fe, as shown in the work on bacterial reaction centers (2), removes this magnetic coupling, allowing the investigation of the semiquinone states. Removal of Fe from Photosystem II has already been described (3).
KeywordsMagnetic Coupling ENDOR Spectrum Bacterial Reaction Center Electron Nuclear Double Resonance Charge Separation Process
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