title: The S0 state of photosystem II induced by hydroxylamine: differences between the structure of the manganese complex in the S0 and S1 states determined by X-ray absorption spectroscopy.
abstract: Hydroxylamine at low concentrations causes a two-flash delay in the first maximum flash yield of oxygen evolved from spinach photosystem II (PSII) subchloroplast membranes that have been excited by a series of saturating flashes of light. Untreated PSII membrane preparations exhibit a multiline EPR signal assigned to a manganese cluster and associated with the S2 state when illuminated at 195 K, or at 273 K in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). We used the extent of suppression of the multiline EPR signal observed in samples illuminated at 195 K to determine the fraction of PSII reaction centers set back to a hydroxylamine-induced S0-like state, which we designate S0*. The manganese K-edge X-ray absorption edges for dark-adapted PSII preparations with or without hydroxylamine are virtually identical. This indicates that, despite its high binding affinity to the oxygen-evolving complex (OEC) in the dark, hydroxylamine does not reduce chemically the manganese cluster within the OEC in the dark. After a single turnover of PSII, a shift to lower energy is observed in the inflection of the Mn K-edge of the manganese cluster. We conclude that, in the presence of hydroxylamine, illumination causes a reduction of the OEC, resulting in a state resembling S0. This lower Mn K-edge energy of S0*, relative to the edge of S1, implies the storage and stabilization of an oxidative equivalent within the manganese cluster during the S0----S1 state transition. An analysis of the extended X-ray absorption fine structure (EXAFS) of the S0* state indicates that a significant structural rearrangement occurs between the S0* and S1 states. The X-ray absorption edge position and the structure of the manganese cluster in the S0* state are indicative of a heterogeneous mixture of formal valences of manganese including one Mn(II) which is not present in the S1 state.
authors.affiliation: Lawrence Berkeley Laboratory, Department of Chemistry, University of California, Berkeley 94720.
authors.forename: R D
authors.initials: RD
authors.lastname: Guiles
authors.forename: V K
authors.initials: VK
authors.lastname: Yachandra
authors.forename: A E
authors.initials: AE
authors.lastname: McDermott
authors.forename: J L
authors.initials: JL
authors.lastname: Cole
authors.forename: S L
authors.initials: SL
authors.lastname: Dexheimer
authors.forename: R D
authors.initials: RD
authors.lastname: Britt
authors.forename: K
authors.initials: K
authors.lastname: Sauer
authors.forename: M P
authors.initials: MP
authors.lastname: Klein
mesh_terms: D002734:Chlorophyll / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D005583:Fourier Analysis; D019811:Hydroxylamine; D006898:Hydroxylamines / Q000494:pharmacology*; D008027:Light; D045342:Light-Harvesting Protein Complexes; D008345:Manganese / Q000378:metabolism*; D010084:Oxidation-Reduction; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins / Q000378:metabolism*; D013057:Spectrum Analysis; D014965:X-Rays
chemical_list: D006898:Hydroxylamines; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D002734:Chlorophyll; D019811:Hydroxylamine; D008345:Manganese