Two stages in the formation of active plasma thromboplastin

Although the exact role of calcium in the complex mechanism of blood coagulation is still in some dispute, it is certain that it is a basic element in some of the interactions taking place between the various blood-clotting factors which finally lead to the formation of the prothrombin-converting factor, plasma thromboplastin1. Recently, we2 described an ether-precipitation method for the separation of the latter. Further work, reported herein, on the relation between this important blood-clotting factor and calcium has revealed the presence of two stages in the production of a fully active plasma thromboplastin.