The formation of ferritin from apoferritin. Inhibition and metal ion-binding studies.

Inhibition by Zn(2+) of iron uptake by apoferritin at very low substrate concentrations is shown to be competitive. It is proposed that Zn(2+) competes with Fe(2+) for sites on the protein at which the oxidation of Fe(2+) is catalysed. Interpretation of titration data suggests there are two independent classes of binding site for Zn(2+) and several other cations. Sites in one such class are probably on the external surface of the apoferritin molecule. The catalytic binding sites are presumed to be internal and may involve histidine or possibly cysteine as ligands.