ferritin

Ferritin is a family of iron-storage proteins found in most living organisms. In animals, ferritin stores iron in a soluble, non-toxic form and releases it in a controlled way to meet cellular needs. The ferritin protein assembles into a 24-subunit shell that forms a hollow nanocage capable of storing up to about 4,500 iron atoms as an iron oxide mineral core.

Most mammalian ferritin is built from two types of subunits, H and L. The H-subunit provides ferroxidase activity that catalyzes conversion of Fe2+ to Fe3+, aiding rapid iron uptake; the L-subunit promotes iron nucleation and long-term storage. The ratio of subunits varies by tissue and developmental stage.

Ferritin is found in the cytosol of most cells and is abundant in the liver, spleen, and bone marrow. The serum form, derived mainly from macrophages and hepatocytes, is used clinically as an indicator of total body iron stores, though ferritin is also an acute-phase protein whose levels rise in inflammation, infection or liver disease, potentially masking iron deficiency.

Iron homeostasis involves regulation of ferritin synthesis by iron-regulatory proteins and binding of iron to the storage core, as well as iron export via ferroportin and regulation by hepcidin. When iron is needed, ferritin can be degraded by ferritinophagy, a selective autophagy process mediated by NCOA4, releasing iron for metabolic use.

Beyond physiology, ferritin-like nanocages are explored in nanotechnology for drug delivery, imaging, and as scaffolds for biomineralization due to their stability and uniform size.