title: The origin of split EPR signals in the Ca2+-depleted photosystem II.
abstract: A light-driven reaction model for the Ca2+-depleted Photosystem (PS) II is proposed to explain the split signal observed in electron paramagnetic resonance (EPR) spectra based on a comparison of EPR assignments with recent x-ray structural data. The split signal has a splitting linewidth of 160 G at around g = 2 and is seen upon illumination of the Ca2+-depleted PS II in the S2 state associated with complete or partial disappearance of the S2 state multiline signal. Another g=2 broad ESR signal with a 110 G linewidth was produced by 245 K illumination for a short period in the Ca2+-depleted PS II in S1 state. At the same time a normal YZ . radical signal was also efficiently trapped. The g=2 broad signal is attributed to an intermediate S1X. state in equilibrium with the trapped YZ . radical. Comparison with x-ray structural data suggests that one of the split signals (doublet signal) is attributable to interaction between His 190 and the YZ . radical, and other signals is attributable to interaction between His 337 and the manganese cluster, providing further clues as to the mechanism of water oxidation in photosynthetic oxygen evolution.
authors.affiliation: Division of Material Science (Physics), Graduate school of Science, Nagoya University, Furou, Chikusa, Nagoya 464-8602, Japan. mino@bio.phys.nagoya-u.ac.jp
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Mino
authors.forename: Shigeru
authors.initials: S
authors.lastname: Itoh
mesh_terms: D002118:Calcium / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D004735:Energy Transfer; D008027:Light; D008956:Models, Chemical; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000378:metabolism*; D018724:Spinacia oleracea / Q000378:metabolism
chemical_list: D045332:Photosystem II Protein Complex; D002118:Calcium