transferrina

Transferrin is a secreted glycoprotein produced mainly by the liver and circulating in blood plasma. It is the principal iron-transport protein in humans, binding ferric iron (Fe3+) at two high-affinity sites per molecule and delivering iron to cells throughout the body. In its iron-free form (apo-transferrin) it circulates until it binds iron, forming holo-transferrin.

Each transferrin molecule has two lobes, and each lobe can bind one Fe3+ ion in the presence of a synergistic anion such as carbonate. Transferrin delivers iron by binding to the transferrin receptor on cells, typically transferrin receptor 1 (TfR1). The complex is taken into cells by receptor-mediated endocytosis. In the acidic environment of the endosome, iron is released, reduced to Fe2+, and transported into the cytosol, while apo-transferrin remains bound to the receptor and is recycled to the cell surface, where it is released back into circulation at physiological pH.

Regulation and physiology: transferrin synthesis is influenced by iron status, nutritional state, and inflammatory signals; it is generally considered a negative acute-phase protein, with levels falling during inflammation. The concentration of transferrin in plasma and the related measure known as total iron-binding capacity (TIBC) reflect the body’s capacity to transport iron. The transferrin saturation percentage, calculated from serum iron and TIBC, indicates how much of transferrin’s iron-binding sites are occupied.

Clinical relevance: abnormal transferrin levels or saturation are used in iron studies to diagnose iron deficiency, iron overload, and certain liver or nutritional disorders. Rare genetic defects can cause af transferrin-emia, a condition characterized by severely reduced transferrin and iron transport.