Stores iron in a soluble, non-toxic, readily available form. Important for iron homeostasis. Has ferroxidase activity. Iron is taken up in the ferrous form and deposited as ferric hydroxides after oxidation (By similarity). 4 Fe(2+) + 4 H(+) + O2 = 4 Fe(3+) + 2 H2O Oligomer of 24 subunits. The functional molecule forms a roughly spherical shell with a diameter of 12 nm and contains a central cavity into which the insoluble mineral iron core is deposited (By similarity). Belongs to the ferritin family.