A procoagulant protein was isolated from Vipera aspis aspis (Aspic viper) venom by Sephadex G-75, DEAE-Sephacel, Q-Sepharose and Sephadex G-150 column chromatography. 2. The purified protein has a molecular weight of 125,000 and an isoelectric point of 4.3. 3. This procoagulant decreased the clotting time of plasma from humans, however, direct fibrongen clotting activity was not detected. 4. Diisopropyl fluorophosphate, a serine-protease inhibitor affected coagulant activity of purified protein significantly, while a factor Xa inhibitor (3-ABPE) possessed a slight inhibitory effect. 5. Bovine prothrombin incubated with isolated protein, phospholipid emulsion, bovine factor V and calcium ions drastically decreased the clotting time of fibrinogen and expressed hydrolytic activity against synthetic arginine esterase substrates. However, no hydrolytic activity these substrates was detected with the procoagulant alone indicating that this protein might participate in activation of prothrombin.
