Conversion of Prothrombin to Autoprothrombin II (Platelet Cofactor II) and Its Relation to the Blood Clotting Mechanisms

¹ From the Department of Physiology and Pharmacology, Wayne University College of Medicine, Detroit, Michigan

Under certain restricted conditions purified thrombin can be added to purified prothrombin and the latter transforms to a derivative called autoprothrombin II. Except in 25% sodium citrate solution, it has not been converted to thrombin. It functions as a cofactor with purified platelet factor 3 in the conversion of prothrombin to thrombin. Serum from healthy persons and in hemophilia A contains autoprothrombin II activity that can be adsorbed on BaCO₃. Autoprothrombin II, prepared in the laboratory, can be added to the two types of adsorbed serum and the autoprothrombin II activity is restored to the serum. Serum from PTA patient, and a patient receiving dicumarol was found to contain very little autoprothrombin II activity. By adding an appropriate quantity of autoprothrombin II, prepared in the laboratory, the autoprothrombin II activity of the PTC serum was not completely restored whereas it was with the other two serum samples.

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