[Is platelet protein S different from plasma protein S in human being?]

Platelet suspension was obtained from normal platelet rich plasma (PRP) by the gel filtration method using Sepharose 2B and platelet pellet was prepared from the platelet suspension after centrifugation. A platelet preparation was prepared from the solubilized platelet pellet. Purified protein S was obtained from plasma and platelet preparation using immuno-affinity column chromatography. Total antigen of protein S was measured by enzyme immunoassay and activity of protein S was measured as a cofactor of activated protein C. The ratio of purified protein S activity to total antigen in normal plasma and platelet was 2.3 and 2.1, respectively. According to immunoblot and crossed immunoelectrophoresis studies, the molecular weight of platelet protein S was different from that of plasma protein S. Localization of protein S in platelet alpha-granules was demonstrated by immunoelectronmicroscopy.