Urokinase-type plasminogen activator is a strong plasminogen activator which specifically cleaves the proenzyme/zymogen plasminogen to form the active enzyme plasmin. It specifically catalyzes the cleavage of the arg-|-val bond in plasminogen. The active plasmin is then able to break down the fibrin polymers of blood clots. Clinically, urokinase-type plasminogen activator is given to patients suffering from thrombolytic disorders.

The amino terminal fragment (ATF) of urokinase-type plasminogen activator is 130 amino acid residues long. It consists of 2 alpha-helices (green) and 2 antiparallel beta-strands (purple). The ATF contains 2 domains; a growth factor domain and a kringle domain. It binds fucose (magenta) as a ligand.