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. 4 Fe(2+) + 4 H(+) + O2 = 4 Fe(3+) + 2 H2O Oligomer of 24 subunits. The functional molecule is roughly spherical and contains a central cavity into which the polymeric mineral iron core is deposited. There are three types of ferritin subunits in amphibia: L, M and H chains. M and H chains are fast mineralizing; the L chain is very slow mineralizing. Belongs to the ferritin family.