A comparison of the abilities of plasma kallikrein, beta-Factor XIIa, Factor XIa and urokinase to activate plasminogen.

In order to compare the relative potencies of plasma kallikrein, beta-Factor XIIa, Factor XIa and urokinase as plasminogen activators, plasminogen activation by these proteins was studied using a radiolabeled fibrin plate assay. Urokinase was approximately 20,000 times more active than kallikrein or Factor XIa and 300,000 times more active than beta-Factor XIIa. Kallikrein and Factor XIa were approximately equal in plasminogen activator activity and were 20 times more potent than beta-Factor XIIa.