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 formed in the supernatant solution of activitated platelets and has an apparent mass of 77 kd (2,3,4). Protein nexin I also forms a similar size complex with thrombin (5). However, apparent differences between these two nexins (4), as well as difficulties in purifying the platelet nexin, have prevented the identification of the platelet nexin. We purified the nexin from the supernatant solution of activated platelets and identified it as protease nexin I (PNIp). The two components in the 77 kd complex are thrombin and PNIp.