title: Towards a spin coupling model for the Mn4 cluster in Photosystem II.
abstract: The X-band EPR spectra of the IR sensitive untreated PSII and of MeOH- and NH(3)-treated PSII from spinach in the S(2)-state are simulated with collinear and rhombic g- and Mn-hyperfine tensors. The obtained principal values indicate a 1Mn(III)3Mn(IV) composition for the Mn(4) cluster. The four isotropic components of the Mn-hyperfine tensors are found in good agreement with the previously published values determined from EPR and (55)Mn-ENDOR data. Assuming intrinsic isotropic components of the Mn-hyperfine interactions identical to those of the Mn-catalase, spin density values are calculated. A Y-shape 4J-coupling scheme is explored to reproduce the spin densities for the untreated PSII. All the required criteria such as a S=1/2 ground state with a low lying excited spin state (30 cm(-1)) and an easy conversion to a S=5/2 system responsible for the g=4.1 EPR signal are shown to be satisfied with four antiferromagnetic interactions lying between -290 and -130 cm(-1).
authors.affiliation: Laboratoire de Chimie Inorganique, UMR 8613, LRC-CEA no. 33V, Institut de Chimie Moléculaire et des Matériaux d'Orsay, Université Paris-Sud, 91405 Orsay Cedex, France.
authors.forename: Marie-France
authors.initials: MF
authors.lastname: Charlot
authors.forename: Alain
authors.initials: A
authors.lastname: Boussac
authors.forename: Geneviève
authors.initials: G
authors.lastname: Blondin
mesh_terms: D000641:Ammonia / Q000494:pharmacology; D004578:Electron Spin Resonance Spectroscopy; D008345:Manganese / Q000737:chemistry*; D000432:Methanol / Q000494:pharmacology; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000187:drug effects; D018724:Spinacia oleracea
chemical_list: D045332:Photosystem II Protein Complex; D008345:Manganese; D000641:Ammonia; D000432:Methanol