Catalyzes the oxidation of ferrous iron(II) to ferric iron(III) and stores iron in a soluble, non-toxic, readily available form (PubMed:11323407, PubMed:15201052). Important for iron homeostasis (PubMed:11323407, PubMed:15201052). Iron is taken up in the ferrous form and deposited as ferric hydroxides after oxidation (PubMed:11323407, PubMed:15201052). 4 Fe(2+) + 4 H(+) + O2 = 4 Fe(3+) + 2 H2O Homooligomer of 24 subunits. The functional molecule is roughly spherical and contains a central cavity into which the polymeric mineral iron core is deposited. Detected in testis and erythroleukemia. Expression is very low or not detectable in brain, colon, heart, kidney, liver, lung, muscle, placental, spleen and small intestine. Belongs to the ferritin family. Ferritin entry