Iron Oxidation in Sheep, Horse and Recombinant Human Apoferritins

Abstract

Knowledge of the iron oxidation reactions which occur during core formation in ferritin is central to understanding the mechanism of iron biomineralization within the protein. Recent studies have shown that there are two principal kinetic pathways of iron oxidation in horse spleen apoferritin, ^1,2 the protein catalysis and crystal growth mechanisms proposed over a decade ago. ^3,4 In the protein catalysis pathway, the net iron(II) oxidation reaction is given by equation 1. This pathway is dominant when small increments of Fe²⁺

$$ 2F{{e}^{{2 + }}}{{O}_{2}} + 4{{H}_{2}}O \to 2FeOO{{H}_{{core}}} + {{H}_{2}}{{O}_{2}} + 4{{H}^{ + }} $$

((1))

are introduced to the protein, i. e., < 50 Fe²⁺/protein. Here, hydrogen peroxide is the principal product of dioxygen reduction. Once produced, the H₂O₂ undergoes the disproportion reaction 2 to form dioxygen and water over a period of 30 minutes.² Superoxide O₂ ^- does not appear to be a product of dioxygen reduction^1,5 nor is it an effective oxidant of Fe²⁺ in apoferritin compared to O₂.²