PURIFICATION OF SECRETED PLATELET PROTEASE NEXIN-I

Thrombin, a platelet agonist which also has biological effects towards other cells, forms complexes with platelet proteins which may affect its activity (1). One such complex with platelet protease nexin is for med in the supernatant solution of activitated platelets and has an ap parent mass of 77 kd (2,3,4). Protein nexin I also forms a similar siz e complex with thrombin (5). However, apparent differences between the se two nexins (4), as well as difficulties in purifying the platelet n exin, have prevented the identification of the platelet nexin. We puri fied the nexin from the supernatant solution of activated platelets an d identified it as protease nexin I (PNIp). The two components in the 77 kd complex are thrombin and PNIp.