FTIR spectroelectrochemistry combined with a light-induced difference technique: Application to the iron-quinone electron acceptor in photosystem II

Photosystem II (PSII) in plants and cyanobacteria performs light-driven water oxidation to obtain electrons necessary for CO2 fixation. In PSII, a series of electron transfer reactions take place from the Mn4CaO5 cluster, the catalytic site of water oxidation, to a plastoquinone molecule via several redox cofactors. Light-induced Fourier transform infrared (FTIR) difference spectroscopy has been extensively used to investigate the structures and reactions of the redox cofactors in PSII. Recently, FTIR spectroelectrochemistry combined with the light-induced difference technique was applied to study the mechanism of electrontransfer regulation in PSII involving the quinone electron acceptors, QA and QB, and the non-heme iron that bridges them. In this mini-review, this combined FTIR method is introduced, and obtained results about the redox reactions of the non-heme iron and QB, involving the long-range interaction of the Mn4CaO5 cluster with the electron-acceptor side, are summarized.