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

Abstract

Abstract. Photosystem II (PSII) in plants and cyanobacteria performs light-driven water oxidation to obtain electrons necessary for CO 2 fixation. In PSII, a series of electron transfer reactions take place from the Mn 4 CaO 5 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, Q A and Q B , 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 Q B , involving the long-range interaction of the Mn 4 CaO 5 cluster with the electron-acceptor side, are summarized.

Inhibitory and Non-Inhibitory NH3 Binding at the Water-Oxidizing Manganese Complex of Photosystem II Suggests Possible Sites and a Rearrangement Mode of Substrate Water Molecules

“…Similar spectral changes that can be assigned to the oxidation of Fe 2+ to Fe 3+ have been described before for the PSII membrane particles 74−76 and cyanobacterial PSII. 77,78 In the work presented here, we use the magnitude of these acceptor side redox features to assess the number of electrons transferred from the donor to the acceptor side of PSII.…”

Protonation State of a Key Histidine Ligand in the Iron–Quinone Complex of Photosystem II as Revealed by Light-Induced ATR-FTIR Spectroscopy

“…However, D1-H215 was not assumed to be a titratable group in this calculation, and hence, the contribution of D1-H215 was not involved in the calculated results. Further studies using FTIR spectroelectrochmistry , are necessary to investigate the direct correlation between the protonation state of D1-H215 and the change in E m (Fe 2+ /Fe 3+ ) and the possible contributions of carboxylate groups around the non-heme iron in the pH dependence of E m (Fe 2+ /Fe 3+ ). Examination of the pH dependence of proton release upon iron oxidation, which was previously detected at pH 8 using buffer bands, may also provide crucial information.…”

pH-Dependent Regulation of the Relaxation Rate of the Radical Anion of the Secondary Quinone Electron Acceptor QB in Photosystem II As Revealed by Fourier Transform Infrared Spectroscopy

“…Light-induced Fourier transform infrared (FTIR) difference spectroscopy is a powerful method for investigating the electron transfer and water oxidation reactions in PSII. − With this method, the redox reactions of Q A and Q B can be separately monitored using their specific signals at ∼1717 and ∼1745 cm –1 , respectively, which arise from the 13 2 -ester CO vibrations of nearby Pheo D1 and Pheo D2 , respectively, having different hydrogen bonding interactions . These Pheo signals in the Q A – /Q A and Q B – /Q B difference spectra are directly coupled with formation of Q A – and Q B – , respectively, and thus are useful markers for detecting them.…”