title: Fe2+ binding to apo and holo mammalian ferritin.
abstract: The binding of Fe2+ to both apo and holo mammalian ferritin has been investigated under anaerobic conditions as a function of pH. In the pH range 6.0-7.5, 8.0 +/- 0.5 Fe2+ ions bind to each apoferritin molecule, but above pH 7.5, a pH-dependent Fe2+ binding profile is observed with up to 80 Fe2+ ions binding at pH 10.0. This Fe2+ binding is reversible and is accompanied by up to two H+ being released per Fe2+ bound at pH 10.0. The Fe2+ binding to apoferritin probably occurs in the 3-fold channels. A much larger and more complex pH-dependent Fe2+ binding stoichiometry was observed for holoferritin with up to 300 Fe2+ ions binding at pH 10.0. This pH-dependent Fe2+ binding was interpreted as Fe2+ interaction at the FeOOH mineral surface with displacement of H+ from -OH or phosphate surface groups by the incoming Fe2+ ions. Mossbauer spectroscopic measurements using 57Fe-labeled Fe2+ under anaerobic conditions showed that 57Fe2+ binding to holoferritin was accompanied by electron transfer to the core, yielding 57Fe3+, presumably bound to the mineral surface. Removal of added iron by Fe2+-specific chelating agents yielded 57Fe2+, demonstrating the reversibility of this electron-transfer process. The Fe2+ bound to apo- and holoferritin is readily converted to Fe3+ by exposure to O2 and strongly retained by the respective ferritin species.
authors.affiliation: Battelle Memorial Institute, Columbus, Ohio 43201.
authors.forename: D
authors.initials: D
authors.lastname: Jacobs
authors.forename: G D
authors.initials: GD
authors.lastname: Watt
authors.forename: R B
authors.initials: RB
authors.lastname: Frankel
authors.forename: G C
authors.initials: GC
authors.lastname: Papaefthymiou
mesh_terms: D000818:Animals; D001052:Apoferritins / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D005293:Ferritins / Q000031:analogs & derivatives* / Q000378:metabolism*; D006736:Horses; D006859:Hydrogen / Q000493:pharmacokinetics; D007501:Iron / Q000378:metabolism*; D015204:Spectroscopy, Mossbauer
chemical_list: D006859:Hydrogen; D005293:Ferritins; D001052:Apoferritins; D007501:Iron