THE FUNCTION OF H AND L CHAINS IN IRON SEQUESTRATION IN FERRITIN

In order to understand the iron sequestering mechanism within the prot ein shell in ferritins, Mossbauer studies were performed on horse sple en ferritin (about 15% H and 85% L chains) and variants of human H cha in ferritins in which putative oxidation and nucleation site ligands h ave been changed by site directed mutagenesis and which were loaded wi th small amounts of iron and frozen at short times after iron loading. It was found that the catalysis by apoferritin of Fe(II) oxidation is associated with residues within the H chains, that both Fe(III) monom ers and dimers are located on H chains and that these dimers form at f erroxidase centers. Nevertheless iron core formation does occur also i n ferritins that lack the ferroxidase center of the H chains, though i nitial Fe(II) oxidation is slower.