Journal
BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS
Volume 1847, Issue 1, Pages 35-45Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.bbabio.2014.06.009
Keywords
FTIR; Time-resolved infrared spectroscopy; Photosynthesis; Water oxidation; Oxygen evolution; Proton transfer
Categories
Funding
- Ministry of Education, Culture, Sports, Science, and Technology [24000018, 24107003, 25291033]
- Grants-in-Aid for Scientific Research [24000018, 24107003] Funding Source: KAKEN
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Photosynthetic water oxidation, which provides the electrons necessary for CO2 reduction and releases O-2 and protons, is performed at the Mn4CaO5 cluster in photosystem II (PSII). In this review, studies that assessed the mechanism of water oxidation using infrared spectroscopy are summarized focusing on electron and proton transfer dynamics. Structural changes in proteins and water molecules between intermediates known as Si states (i = 0-3) were detected using flash-induced Fourier transform infrared (FTIR) difference spectroscopy. Electron flow in PSII and proton release from substrate water were monitored using the infrared changes in ferricyanide as an exogenous electron acceptor and Mes buffer as a proton acceptor. Time-resolved infrared (TRIR) spectroscopy provided information on the dynamics of proton-coupled electron transfer during the S-state transitions. In particular, a drastic proton movement during the lag phase (similar to 200 mu s) before electron transfer in the S-3 --> S-0 transition was detected directly by monitoring the infrared absorption of a polarizable proton in a hydrogen bond network. Furthermore, the proton release pathways in the PSII proteins were analyzed by FTIR difference measurements in combination with site-directed mutagenesis, isotopic substitutions, and quantum chemical calculations. Therefore, infrared spectroscopy is a powerful tool for understanding the molecular mechanism of photosynthetic water oxidation. This article is part of a Special Issue entitled: Vibrational spectroscopies and bioenergetic systems. (C) 2014 Elsevier B.V. All rights reserved.
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