The urokinase enzyme is a serine protease released by the kidney and is aimportant member of the Pulmonary renal cascade. The uPA system consists of the serine proteinases uPA and plasmin, two serpin plasminogen activator inhibi¬tors (PAI; PAI-1 and PAI-2), the serpin plasmin inhibitor α2-anti-plasmin, and the cell surface uPA receptor (uPAR), a member of the glycosylphosphatidylinositol (GPI)-anchored protein family. There are two types of plasminogen activators (PAs): tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA), both of which can catalyze the conversion of the inactive plasminogen zymogen to plasmin, as well as cause the activation of additional protease zymogens and other latent growth factors. Urokinaseis structurally unique and does contribute to multiple physiological roles and its effects are also prominent on the pulmonary system whereby along with the erythropoietin and heparin binding growth factors it plays a critical role in the pulmonary renal cascade.
