We have investigated the reaction products of several iron(III) compounds with hydrogen peroxide, and have found that hydrogen peroxide promotes the formation of an oxo-bridged iron(III) species in the presence of methanol (electron donor), and carboxyl groups of the ligand systems play a role to give the tetranuclear iron(III) compound containing a bent Fe-O-Fe unit (O: oxo oxygen atom). Based on the present results and the facts that L-chains of human ferritins lack ferroxidase activity, but are richer in carboxyl groups (glutamates) exposed on the cavity surface, it seems reasonable to conclude that (i) the hydrogen peroxide released in the H-subunit may contribute to the formation of a diferric oxo-hydrate in the L-subunit, (ii) the formation of a bent oxo-bridged iron(III) species is essentially important in the L-subunit, and (iii) rich carboxyl groups in L-subunits contribute to facilitate iron nucleation and mineralization through the capture and activation of the peroxide ion, and formation of a stable bent oxo-bridged iron(III) species.
We have found that deposition of the iron(III) hydroxide occurred rapidly on the aggregates of amyloid beta-peptide (1-40), transferrin, and albumin induced by zinc(II) chloride in the solution containing iron(III) compounds with amino acid derivatives; the deposition of iron(III) hydroxide may proceed via the coordination of nitrogen and oxygen atoms of the amino acid residues of the aggregated proteins to the iron(III) ion, implying that iron(III) compounds with amino acids or peptides in plasma, so-called "non-specific iron," should be an intrinsic iron(III)-ion carrier to induce the high level accumulation of iron(III) ions in the amyloid deposits.
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