[Fibrinolytic activity of acyl-urokinase]

Urokinase was acylated at the active site serine hydroxyl using p-amidinophenyl benzoate or p-nitrophenyl p'-guanidinobenzoate. The enzymatically inactive acyl-urokinase was reactivated in buffer (pH 7.5) or plasma at 37 degrees C with a half-life of 11 min (benzoyl-urokinase) or 10 h (p-guanidinobenzoyl-urokinase). Upon administration (50,000 IU/kg) to rabbits, urokinase was more rapidly eliminated than either acyl-enzyme. The results suggest that urokinase is eliminated via the binding to plasma inhibitors.