Ferritin

Ferritin is a universal intracellular and extracellular protein that stores iron and releases it in a controlled fashion. The protein is produced by almost all living organisms, including archaea, bacteria, algae, higher plants, and animals. It is the primary intracellular iron-storage protein in both prokaryotes and eukaryotes, keeping iron in a soluble and non-toxic form. In humans, it acts as a buffer against iron deficiency and iron overload. Ferritin is found in most tissues as a cytosolic protein, but small amounts are secreted into the serum where it functions as an iron carrier. Plasma ferritin is also an indirect marker of the total amount of iron stored in the body; hence, serum ferritin is used as a diagnostic test for iron-deficiency anemia and iron overload. Aggregated ferritin transforms into a water-insoluble, crystalline and amorphous form of storage iron called hemosiderin. Ferritin is a globular protein complex consisting of 24 protein subunits forming a hollow spherical nanocage with multiple metal–protein interactions. Ferritin with iron removed is called apoferritin.