Pharmacology of thrombolysis: urokinase.

and animal plasminogen into plasmin (Fig. 1) as well as the hydrolysis of lysine and arginine esters; the esterolytic activity of the activator, in contrast to plasmin, is not inhibited by soybean trypsininhibitor. Its active site is not accessible to bigger molecules, as evidenced-by a strong reduction of its proteolytic activity compared with plasmin. Fibrin, for example, is cleaved not at all by the SK-induced activator. Plasmin also combines with SK to form an activator complex. It is suggested that the activator has an active site in common with plasmin, with the difference that it is partially sterically blocked by SK. This would explain that the esterolytic activity of the SK-induced activator equals the activity of plasmin, but that the esterolytic activity of the activator is not abolished by soybean trypsininhibitor and that large protein molecules are not cleaved in contrast to plasmin. It remains still to be explained how the active site is generated from PP by SK. An autocatalytic process triggered by SK may be assumed.