title: EPR characterisation of the triplet state in photosystem II reaction centers with singly reduced primary acceptor Q(A).
abstract: The triplet states of photosystem II core particles from spinach were studied using time-resolved cw EPR technique at different reduction states of the iron--quinone complex of the reaction center primary electron acceptor. With doubly reduced primary acceptor, the well-known photosystem II triplet state characterised by zero-field splitting parameters |D|=0.0286 cm(-1), |E|=0.0044 cm(-1) was detected. When the primary acceptor was singly reduced either chemically or photochemically, a triplet state of a different spectral shape was observed, bearing the same D and E values and characteristic spin polarization pattern arising from RC radical pair recombination. The latter triplet state was strongly temperature dependent disappearing at T=100 K, and had a much faster decay than the former one. Based on its properties, this triplet state was also ascribed to the photosystem II reaction center. A sequence of electron-transfer events in the reaction centers is proposed that explains the dependence of the triplet state properties on the reduction state of the iron--quinone primary acceptor complex.
authors.affiliation: Department of Biophysics, Huygens Laboratory, P.O. Box 9504, 2300 RA Leiden, The Netherlands.
authors.forename: W Onno
authors.initials: WO
authors.lastname: Feikema
authors.forename: Peter
authors.initials: P
authors.lastname: Gast
authors.forename: Irina B
authors.initials: IB
authors.lastname: Klenina
authors.forename: Ivan I
authors.initials: II
authors.lastname: Proskuryakov
mesh_terms: D016227:Benzoquinones / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D007501:Iron / Q000737:chemistry; D045332:Photosystem II Protein Complex / Q000737:chemistry*; D018724:Spinacia oleracea / Q000201:enzymology*; D013696:Temperature
chemical_list: D016227:Benzoquinones; D045332:Photosystem II Protein Complex; C004532:quinone; D007501:Iron