Kunitz-type inhibitors in human serum. Identification and characterization.

Human serum contains small amounts (approximately 0.1 mg/liter) of two protein protease inhibitors of low molecular weight (approximately 6500) and basic isoelectric point (Kunitz-type). They were purified by affinity chromatography on immobilized trypsin and ion-exchange chromatography in the fast protein liquid chromatography system. Their chemical, immunochemical, and functional properties indicate that the purified inhibitors are highly homologous with the basic pancreatic trypsin inhibitor which is widely distributed in bovids and caprids. Their inhibitory activity toward serine proteases such as plasmin and kallikrein suggests a possible regulatory role in blood clotting and fibrinolysis.