Urokinase (trade name Abbokinase), also called urokinase-type plasminogen activator (uPA), is a serine protease (EC3.4.21.73). It was discovered in 1947 by McFarlane. Urokinase was originally isolated from human urine, but is present in several physiological locations, such as blood stream and the extracellular matrix. The primary physiological substrate is plasminogen, which is an inactive form (zymogen) of the serine protease plasmin. Activation of plasmin triggers a proteolysis cascade that, depending on the physiological environment, participates in thrombolysis or extracellular matrix degradation. This links urokinase to vascular diseases and cancer.