MATERIALS AND METhODS Preparation of Platelet Extract

D URING the last ten years evidence has been presented from different laboratories that fibrinogen may not be essential for thrombin-mediated platelet aggregation.14 Although the presence, in platelets, of a thrombin-sensitive protein other than fibrinogen has been reported from this laboratory and also by other workers,5#{176} there is no report of its isolation, structure, physicochemical properties, mechanism of action with thrombin or possible role in hemostasis. In this study, we report a high degree of resolution of platelet proteins by gel electrophoresis, evidence for more than one thrombin-labile protein other than fibrinogen, and some of the properties of one of these proteins