What is ferritin?

By William Aird

A soluble 450 kiloDalton (kDa) protein found in all cells of the body but in especially high concentrations in macrophages of bone marrow, spleen, and liver. Ferritin is comprised of 24 monomer subunits that consist of either heavy type (21 kDa) or light type (19 kDa) polypeptide chains encoded by 2 different ferritin genes. The 24 monomer subunits associate to form a hollow spherical particle that can store up to 4,000 iron atoms as Fe3+ ions. Ferritin provides intracellular storage of bioavailable iron in a safe and readily accessible form, protecting cells from iron-mediated free radical formation and toxicity.

Structure of the murine ferritin complex. From Wikipedia
Ferritin Structure: Apoferritin forms a roughly spherical container within which ferric iron is stored as a ferrihydrite mineral. Apoferritin refers to the iron-free form of the protein; the iron-containing form is termed holoferritin or simply ferritin. The apoferritin shell is composed of 24 subunits of two types, termed H and L, the ratio of which varies widely depending on tissue type and inflammation. Iron is toxic in cellular systems because of its capacity to generate reactive species (shown as yellow spheres) which can directly damage DNA and proteins. From Knovich et al