Elemental iron is required for a variety of normal cellular functions. It is vital for proper growth and development. Ferritin is the major protein involved in iron sequestration and detoxification. Ferritin is found in all living species. Mammalian liver and spleen ferritin (~450kD) consists of 24 subunits of 2 species. The heavy subunit (~21kD; FTH) and the light subunit (~19kD; FTL). The 2 types of apoferritin subunits were designated H and L for heart and liver, respectively. Ferritin molecules from plants and bacteria contain only H-type chains. 'H-type' is associated with the presence of centers catalyzing the oxidation of two Fe(II) atoms. FTL subunit (rich in human liver and spleen) is coded by a gene in segment 19q13.3. FTH subunit (rich in human heart) is located on chromosome 11. Ferritin is capable of storing up to 4500 atoms of ferric iron. The H-to-L ratio within ferritin varies in a tissue-specific manner. This ratio is also influenced by pathophysiological conditions, including inflammation and malignancy. Hyperferritinemia-cataract syndrome has a mutation in the iron response element (IRE) in the 5-prime noncoding region of the FTL gene. Synthesis of both ferritin subunits is controlled by a common cytosolic protein, iron regulatory proteins (IRPs), which binds to the iron-responsive element (IRE) in the 5'-UTR of the H- and L-ferritin mRNAs. H-chains are important for Fe(II) oxidation. L-chains assist in core formation.