Dysfunctional plasminogen in full term newborn--study of active site of plasmin.

The functional activity and active site of plasmin in full-term newborns have been studied and compared to those in adults in order to investigate the nature of the abnormality found in newborn plasminogen described in a previous paper. The functional activity of newborn plasminogen measured on chromogenic substrate was approximately 18% that of adult plasminogen when streptokinase was used as an activator and 12% when urokinase was used. Proteolysis of newborn plasminogen by urokinase yielding a two-chain plasmin form occurred normally, but the incorporation of diisopropylphosphorofluoridate into the light chain of newborn plasmin was approximately 23% of that observed in the light chain of adult plasmin. These observations suggest that the abnormality of full-term newborn plasminogen is located in the active site of the molecule.