title: Structural and functional modifications of the manganese cluster in Ca(2+)-depleted S1 and S2 states: electron paramagnetic resonance and X-ray absorption spectroscopy studies.
abstract: The effect of extraction of weakly bound Ca2+ by low-pH treatment on the O2-evolving apparatus was studied by use of low-temperature electron paramagnetic resonance (EPR) and X-ray absorption spectroscopy. In low-pH-treated PSII membranes, an S2 EPR multiline signal with modified line shape was induced by illumination at 0 degrees C, but its signal amplitude decreased upon lowering the excitation temperature with concomitant oxidation of cytochrome (cyt) b-559 in place of Mn. The half-inhibition temperature for formation of the modified multiline signal was found at -33 degrees C, which was much higher than that for formation of the normal S2 state in untreated control membranes. Signal IIf was normally induced down to -30 degrees C, but its dependence on excitation temperature was different from that for modified S2. This was interpreted as indicating that the low-temperature blockage of modified S2 formation is due to the incapability of electron abstraction from the Mn cluster. The Mn K-edge of X-ray absorption near-edge structure (XANES) spectrum shifted to lower energy by 0.8 eV after low-pH treatment, but the shift was reversed by addition of Ca2+. Upon illumination at 0 degrees C of treated membranes, the K-edge energy was up-shifted by 0.8 eV, but was not upon illumination at 210 K. These results were interpreted as indicating that extraction of weakly bound Ca2+ by low-pH treatment gives rise to structural and functional modulations of the Mn cluster.
authors.affiliation: Solar Energy Research Group, Institute of Physical and Chemical Research (RIKEN), Saitama, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Ono
authors.forename: M
authors.initials: M
authors.lastname: Kusunoki
authors.forename: T
authors.initials: T
authors.lastname: Matsushita
authors.forename: H
authors.initials: H
authors.lastname: Oyanagi
authors.forename: Y
authors.initials: Y
authors.lastname: Inoue
mesh_terms: D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000737:chemistry; D003573:Cytochrome b Group / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D006863:Hydrogen-Ion Concentration; D008345:Manganese / Q000737:chemistry* / Q000502:physiology; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000378:metabolism; D045332:Photosystem II Protein Complex; D013052:Spectrometry, X-Ray Emission; D013329:Structure-Activity Relationship; D013816:Thermodynamics
chemical_list: D003573:Cytochrome b Group; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D008345:Manganese; C019313:cytochrome b559; D002118:Calcium