title: Proximity of the manganese cluster of photosystem II to the redox-active tyrosine YZ.
abstract: Electron spin echo electron-nuclear double resonance (ESE-ENDOR) experiments performed on a broad radical electron paramagnetic resonance (EPR) signal observed in photosystem II particles depleted of Ca2+ indicate that this signal arises from the redox-active tyrosine YZ. The tyrosine EPR signal width is increased relative to that observed in a manganese-depleted preparation due to a magnetic interaction between the photosystem II manganese cluster and the tyrosine radical. The manganese cluster is located asymmetrically with respect to the symmetry-related tyrosines YZ and YD. The distance between the YZ tyrosine and the manganese cluster is estimated to be approximately 4.5 A. Due to this close proximity of the Mn cluster and the redox-active tyrosine YZ, we propose that this tyrosine abstracts protons from substrate water bound to the Mn cluster.
authors.affiliation: Department of Chemistry, University of California, Davis 95616, USA.
authors.forename: M L
authors.initials: ML
authors.lastname: Gilchrist
authors.forename: J A
authors.initials: JA
authors.lastname: Ball
authors.forename: D W
authors.initials: DW
authors.lastname: Randall
authors.forename: R D
authors.initials: RD
authors.lastname: Britt
mesh_terms: D002118:Calcium / Q000172:deficiency; D004578:Electron Spin Resonance Spectroscopy; D008027:Light; D008345:Manganese; D008667:Metalloproteins / Q000737:chemistry* / Q000378:metabolism / Q000528:radiation effects; D008956:Models, Chemical; D010084:Oxidation-Reduction; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000378:metabolism / Q000528:radiation effects; D045332:Photosystem II Protein Complex; D014443:Tyrosine / Q000737:chemistry* / Q000378:metabolism; D014867:Water / Q000378:metabolism
chemical_list: D008667:Metalloproteins; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D014867:Water; D014443:Tyrosine; D008345:Manganese; D002118:Calcium