transferrine

Transferrin, sometimes spelled transferrine in some languages, is a liver-produced glycoprotein that binds ferric iron (Fe3+) and ferries it through the bloodstream to cells. A typical transferrin molecule contains two high-affinity iron-binding sites, one in each lobed domain. A carbonate ion acts as a synergistic cofactor that stabilizes iron binding at neutral pH. In circulation, iron-loaded transferrin (holotransferrin) interacts with transferrin receptors on cell surfaces, chiefly transferrin receptor 1 (TfR1), and is internalized by receptor-mediated endocytosis. Within the acidic endosome, iron is released and transported into the cytosol, while apotransferrin is recycled back to the cell surface to be reloaded with iron.

Transferrin levels and iron-binding status are central to assessing iron metabolism. Serum transferrin concentration, together with iron, is used to estimate total iron-binding capacity (TIBC) and transferrin saturation, a measure of how much transferrin is carrying iron. Ferritin and inflammatory markers often accompany these tests, since transferrin is a negative acute-phase protein and can decrease during inflammation even when iron stores are sufficient.

Clinical relevance: insufficient transferrin delivery or function can contribute to iron-deficiency anemia, while iron overload disorders typically show high transferrin saturation. Rare hereditary transferrin deficiencies (hypotransferrinemia) have been described. Beyond transport, transferrin is also used in research and therapeutic contexts that exploit the transferrin receptor for cellular entry.

See also: transferrin receptor, iron metabolism, ferritin.