Prothrombin complex proteins as cofactors in platelet aggregation. I. Inhibition of aggregation by antiserum.

Data are presented to support the concept that the vitamin K-dependent coagulation factors are adsorbed onto the platelet membrane and that these make up part of the "plasma atmosphere" necessary for the aggregation of platelets by various agents. Together with evidence that other coagulation factors also are part of the plasma atmosphere, it is suggested that the aggregation reaction is part of the coagulation sequence. The immunologic approach to demonstrating constituents of the platelet membrane promises to be a highly specific technique for studying further the constituents of the platelet membrane and their reactions in hemostasis.