Iron oxidation and hydrolysis reactions of a novel ferritin from Listeria innocua Available to Purchase

Iron deposition in the unusual 12-subunit ferritin from the bacterium Listeria innocua proceeds in three phases: a rapid first phase in which Fe²⁺ binds to the apoprotein, P^Z of charge Z, according to the postulated reaction 2Fe²⁺+P^Z → [Fe₂–P]^Z+2+2H⁺, where [Fe₂–P]^Z+2 represents a dinuclear iron(II) complex formed at each of the 12 ferroxidase centres of the protein; a second phase corresponding to oxidation of this putative complex, i.e. [Fe₂–P]^Z+2+½O₂ → [Fe₂O–P]^Z+2H⁺; and a third phase of iron(II) oxidation/mineralization, i.e. 4Fe²⁺+O₂+8H₂O → 8FeOOH_(s)+8H⁺ [where FeOOH_(s) represents the hydrous ferric oxide mineral that precipitates from the solution], which occurs when iron is added in excess of 24Fe²⁺/protein. In contrast with other ferritins, the ferroxidation reaction in L. innocua ferritin proceeds more slowly than the oxidation/mineralization reaction. Water is the final product of dioxygen reduction in the 12-subunit L. innocua ferritin (the present work) and in the 24-subunit Escherichia coli bacterioferritin, whereas H₂O₂ is produced in 24-subunit mammalian ferritins. Possible reasons for this difference are discussed.