How does the ferritin core form?

Ferritin stores iron as ferrihydrite inside a shell composed of H and L protein chains. H chains contain ferroxidase centres catalysing Fe²⁺ oxidation, while L chains lack these centres but seem to promote ferrihydrite nucleation. Mössbauer spectroscopic studies of recombinant H-chain ferritins show the following: (1) fast Fe²⁺ oxidation is associated with the formation of Fe³⁺ dimers at the ferroxidase centre; (2) within 30 min, a portion of the dimers have split to Fe³⁺ monomers and some monomers have moved to the threefold channels; (3) over longer times, a trend dimer → monomer → core is established. Core formation is accelerated if L chains are present.