title: pH-dependent characteristics of Y(Z) radical in Ca(2+)-depleted photosystem II studied by CW-EPR and pulsed ENDOR.
abstract: The Y(Z)-tyrosine radical was trapped by freezing immediately after illumination in Ca(2+)-depleted Photosystem II (PS II) membranes and the pH-dependent characteristics of the radical were investigated using CW-EPR and pulsed ENDOR. The spectrum of the Y*(Z) radical trapped in the Y*(Z)S(1) state at pH 5.5 was cation-like as reported in Mn-depleted PS II (H. Mino et al., Spectrochim. Acta A 53 (1997) 1465-1483). By illuminating the PS II-retaining S(2) state, the Y*(Z) radical and a broad doublet signal formed in the g approximately 2 region were trapped concomitantly. The spectrum of the trapped Y*(Z) radical in the Y*(Z)S(2) state was cation-like at pH 5.5 but the pulsed ENDOR measurements reveals the involvement of the neutral Y*(Z) radical in the doublet signal. At pH 7.0, the resulting Y*(Z) signal was the mixture of the cation-like and neutral radical spectra, and considerably different from the neutral radical found in Mn-depleted PS II. pH-Dependent changes in the properties of the Y*(Z) radical are discussed in relation to the redox events occurring in Ca(2+)-depleted PS II.
authors.affiliation: Laboratory for Photo-Biology, RIKEN Photodynamics Research Center, The Institute of Physical and Chemical Research, 19-1399 Koeji, Nagamachi, Aoba, Sendai, Japan. mino@postman.riken.go.jp
authors.forename: H
authors.initials: H
authors.lastname: Mino
authors.forename: A
authors.initials: A
authors.lastname: Kawamori
authors.forename: T
authors.initials: T
authors.lastname: Ono
mesh_terms: D002118:Calcium / Q000032:analysis; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D005609:Free Radicals / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008345:Manganese / Q000737:chemistry; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D045332:Photosystem II Protein Complex; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000737:chemistry
chemical_list: D005609:Free Radicals; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; C114979:tyrosyl radical YZ; D014443:Tyrosine; D008345:Manganese; D002118:Calcium