title: Binding of Fe3+ ions to halobacterial purple membranes as studied by Mössbauer spectroscopy.
abstract: Purple membranes (PM) from Halobacterium were reconstituted with 57Fe ions and investigated by Mössbauer spectroscopy within the temperature range from 5 to 300 K at the Fe/bacteriorhodopsin (BR) ratio 0.6-300. When the Fe/Br ratio was below 2, Fe3+ bonded to PM mostly as hydroxymonomeric particle [FeOH]2+.5H2O, the apparent charge of the iron ion being two. When the Fe/BR ratio exceeded two, the dimeric form [FeOH](2+)4.8H2O along with a cluster form dominated. The temperature dependences of the mean square displacement show that the mobility of Fe ions changes from the solid-state type to the quasi-diffusional one at temperatures approximately 200 and approximately 230 K for the dimeric or monomeric and cluster iron forms, respectively. The nature of the cation binding sites and their location on the PM surface are discussed. A possible role of the divalent cation binding to PM in the mechanism of BR proton pumping is suggested.
authors.affiliation: Karpov Physico-Chemical Research Institute, Moscow.
authors.forename: A V
authors.initials: AV
authors.lastname: Maximychev
authors.forename: I G
authors.initials: IG
authors.lastname: Kostyuchenko
authors.forename: F Kh
authors.initials: FKh
authors.lastname: Chibirova
authors.forename: E A
authors.initials: EA
authors.lastname: Zhilinskaya
authors.forename: L N
authors.initials: LN
authors.lastname: Chekulaeva
authors.forename: S F
authors.initials: SF
authors.lastname: Timashev
mesh_terms: D000595:Amino Acid Sequence; D001436:Bacteriorhodopsins / Q000737:chemistry / Q000378:metabolism; D002412:Cations; D003593:Cytoplasm / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D005290:Ferric Compounds / Q000737:chemistry / Q000378:metabolism*; D019617:Halobacterium salinarum / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D008969:Molecular Sequence Data; D017494:Proton Pumps / Q000378:metabolism; D018717:Purple Membrane / Q000737:chemistry / Q000378:metabolism*; D015204:Spectroscopy, Mossbauer; D013696:Temperature
chemical_list: D002412:Cations; D005290:Ferric Compounds; D017494:Proton Pumps; D001436:Bacteriorhodopsins