Summary
Autoprothrombin II-A activity frequently develops when the autoprothrombin II fraction of prothrombin is dried from the frozen state. When the anticoagulant activity develops, the N-terminal amino acid arginine is found, but not when the anticoagulant activity does not develop. The anticoagulant autoprothrombin II-A retarded the conversion of prothrombin to thrombin when three different procoagulants were used; namely, platelet cofactor I, autoprothrombin II, and lung extract. The procoagulant power of the platelet cofactor I is most easily depressed. It is postulated that autoprothrombin II-A activity develops when prothrombin activates and that platelet cofactor I is a receptor of the anticoagulant. In that way the other procoagulants are not ordinarily inhibited by the autoprothrombin II-A. As a further extension of this speculation, attention is brought to the idea that autoprothrombin II-A could be present in certain hemorrhagic diseases. In the PTA patient there is no autoprothrombin II and most likely no autoprothrombin II-A. The close chemical relationship of these two prothrombin derivatives thus may account for the multiple deficiency.
