Snake prothrombin activator that attacks the hemostatic system of prey. This protein is functionally similar to blood coagulation factor Xa. Induces cyanosis and death in mice at 1 mg/kg body weight during blood clotting. Selective cleavage of Arg-|-Thr and then Arg-|-Ile bonds in prothrombin to form thrombin. Activated by calcium and phospholipids. Heterodimer of a light chain and a heavy chain; disulfide-linked. Expressed by the venom gland. Gamma-carboxyglutamate residues are formed by vitamin K dependent carboxylation. These residues are essential for the binding of calcium. The O-linked saccharides at Ser-92 are a mixture of Xyl-Glc, and Glc along with smaller amounts of Xyl-GlcNAc, GlcNAc, Gal, GalNAc, Xyl-Gal, and Xyl-GalNAc, suggesting that the glycosyl transferases responsible for this modification are non-specific. The N-linked carbohydrate at Asn-254 (Asn-45 of the heavy chain) is a sialylated and diantennary oligosaccharide. Is classified in the group D of snake venom prothrombin activators, since it requires the mammalian factor Va for maximal activity for the cleavage of prothrombin. In contrast to blood coagulation factors that circulate as inactive zymogen in plasma, venom prothrombin activators are always found in the active form in the venom. Belongs to the peptidase S1 family. Snake venom subfamily.