Enzymes and Blood Clotting. II. Autoprothrombin C, Russell’s Viper Venom (Stypven), and Trypsin

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Abstract
In its dependence upon prothromboplastic phosphatide and calcium ions, in the conversion of prothrombin to thrombin, Autoprothrombin C is a thromboplastic enzyme. The only other demonstrated accessory factor is V, and any needs for VII, X, XI, or XII are ruled out by the present experiments, as were VIII or IX formerly. The lipid requirement may be satisfied by either phosphatidylserine (PS) or phosphatidylethanolamine (PE), purified from human blood platelets. Comparisons are made with Russell’s viper venom (“stypven”), and with trypsin. The trypsin potentiation of factors VII and X is prevented by pancreatic inhibitor (PI). However, when PI is added after this maximal potentiation, it is no longer inhibitory. The present status of knowledge concerning enzymes in relation to blood coagulation is discussed. * Aided by USPHS Research Grant, H-1510 (CS).