title: Detection of an EPR multiline signal for the S0* state in photosystem II.
abstract: The S0* state was generated by incubation of dark-adapted (S1 state) photosystem II membranes either with the exogenous two electron reductant hydrazine and subsequent 273 K illumination in the presence of DCMU or by dark incubation with low amounts of the one electron reductant hydroxylamine. In agreement with earlier reports, the S1 and S-1 states were found to be electron paramagnetic resonance (EPR) silent. However, in the presence of 0.5-1.5% methanol, a weak EPR multiline signal centered around g = 2.0 was observed at 7 K for the S0* states generated by both procedures. This signal has a similar average line splitting to the well-characterized S2 state multiline EPR signal, but can be clearly distinguished from that and other modified S2 multiline signals by differences in line position and intensities. In addition, at 4 K it can be seen that the S0* multiline has a greater spectral breadth than the S2 multilines and is composed of up to 26 peaks. The S0* signal is not seen in the absence of methanol and is not affected by 1 mM EDTA in the buffer medium. We assign the S0* multiline signal to the manganese cluster of the oxygen evolving complex in a mixed valence state of the form MnIIMnIIIMnIIIMnIII,MnIIMnIIIMnIVMnIV, or MnIIIMnIIIMnIIIMnIV. Addition of methanol may be helpful in future to find an EPR signal originating form the natural S0 state.
authors.affiliation: Department of Biology, Darwin Building, University College London, Gower Street, London WC1E 6BT, UK.
authors.forename: J
authors.initials: J
authors.lastname: Messinger
authors.forename: J H
authors.initials: JH
authors.lastname: Nugent
authors.forename: M C
authors.initials: MC
authors.lastname: Evans
mesh_terms: D004578:Electron Spin Resonance Spectroscopy; D006834:Hydrazines; D019811:Hydroxylamine; D006898:Hydroxylamines; D008345:Manganese; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D045332:Photosystem II Protein Complex; D018724:Spinacia oleracea
chemical_list: D006834:Hydrazines; D006898:Hydroxylamines; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; C029424:hydrazine; D019811:Hydroxylamine; D008345:Manganese