title: The differences in microenvironments and functions of tyrosine radicals YZ and YD in photosystem II studied by EPR.
abstract: Electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) were performed to investigate the difference in microenvironments and functions between tyrosine Z (Y(Z)) and tyrosine D (Y(D)). Mn-depletion or Ca(2+)-depletion causes extension of the lifetime of tyrosine radical Y(Z)(*), which can be trapped by rapid freezing after illumination at about 250 K. Above pH 6.5, Y(Z)(*) radical in Mn-depleted PS II shows similar EPR and ENDOR spectra similar to that of Y(D)(*) radical, which are ascribed to a typical neutral tyrosine radical. Below pH 6.5, Y(Z)(*) radical shows quite different EPR and ENDOR spectra. ENDOR spectra show the spin density distribution of the low-pH form of Y(Z)(*) that has been quite different from the high-pH form of Y(Z)(*). The spin density distribution of the low-pH Y(Z)(*) can be explained by a cation radical or the neutral radical induced by strong electrostatic interaction. The pH dependence of the activation energy of the recombination rate between Y(Z)(*) and Q(A)(-) shows a gap of 4.4 kJ/mol at pH 6.0-6.5. In the Ca(2+)-depleted PS II, Y(Z)(*) signal was the mixture of the cation-like and normal neutral radicals, and the pH dependence of Y(Z)(*) spectrum in Ca(2+)-depleted PS II is considerably different from the neutral radical found in Mn-depleted PS II. Based on the recent structure data of cyanobacterial PS II, the pH dependence of Y(Z)(*) could be ascribed to the modification of the local structure and hydrogen-bonding network induced by the dissociation of ASP170 near Y(Z).
authors.affiliation: Division of Material Science (Physics), Graduate School of Science, Nagoya University, Furocho, Chikusa, Nagoya 464-8602, Japan. mino@bio.phys.nagoya-u.ac.jp
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Mino
authors.forename: Asako
authors.initials: A
authors.lastname: Kawamori
mesh_terms: D002118:Calcium / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D010788:Photosynthesis; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000378:metabolism
chemical_list: D005609:Free Radicals; D045332:Photosystem II Protein Complex; C066447:tyrosyl radical Y(D); C114979:tyrosyl radical YZ; D014443:Tyrosine; D002118:Calcium