title: Substituting Fe for two of the four Mn ions in photosystem II-effects on water-oxidation.
abstract: We have investigated the interaction of Fe(II) cations with Ca-depleted PSII membranes (PSII[-Ca,4Mn]) in the dark and found that Fe(II) incubation removes 2 of 4 Mn ions from the tetranuclear Mn cluster of the photosynthetic O2-evolving complex (OEC). The reduction of Mn ions in PSII(-Ca,4Mn) by Fe(II) and the concomitant release of two Mn(II) cations is accompanied by the binding of newly generated Fe(III) in at least one vacated Mn site. Flash-induced chlorophyll (Chl) fluorescence yield measurements of this new 2Mn/nFe cluster (PSII[-Ca,2Mn,nFe]) show that charge recombination in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) occurs between Qa (-) and the remaining Mn/Fe cluster (but not YZ (●)) in the OEC, and extraction of 2 Mn occurs uniformly in all PSII complexes. No O2 evolution is observed, but the heteronuclear metal cluster in PSII(-Ca,2Mn,nFe) samples is still able to supply electrons for reduction of the exogenous electron acceptor, 2,6-dichlorophrenolindophenol, by photooxidizing water and producing H2O2 in the absence of an exogenous donor as seen previously with PSII(-Ca,4Mn). Selective extraction of Mn or Fe cations from the 2Mn/nFe heteronuclear cluster demonstrates that the high-affinity Mn-binding site is occupied by one of the iron cations. It is notable that partial water-oxidation function still occurs when only two Mn cations are present in the PSII OEC.
authors: BioEnergy Sciences & Technology Directorate, National Renewable Energy Laboratory, Golden, CO, 80401, USA. semin@biophys.msu.ru.|Department of Biophysics, Faculty of Biology, Lomonosov Moscow State University, 119234, Moscow, Russia. semin@biophys.msu.ru.
authors: Boris K
authors: BK
authors: Semin
authors: BioEnergy Sciences & Technology Directorate, National Renewable Energy Laboratory, Golden, CO, 80401, USA.
authors: Michael
authors: M
authors: Seibert
mesh_terms: D001665:Binding Sites; D004579:Electron Transport; D005290:Ferric Compounds / Q000737:chemistry; D007501:Iron / Q000737:chemistry*; D008345:Manganese / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D010788:Photosynthesis; D045332:Photosystem II Protein Complex / Q000737:chemistry*; D018724:Spinacia oleracea; D014867:Water / Q000378:metabolism*
chemical_list: D005290:Ferric Compounds; D045332:Photosystem II Protein Complex; D014867:Water; D008345:Manganese; D007501:Iron; D010100:Oxygen
keywords: Fluorescence yield; Iron; Manganese; Oxygen-evolving complex; Photosystem II