Catalytic subunit of blood coagulation factor X-activating enzyme. Activates coagulation factor X (F10) by cleaving the Arg-Ile bond and is also able to activate coagulation factor IX (F9) and protein S (PROS1) by specific cleavage of Arg-Ile and Arg-Val bonds. Specifically activates several components of the blood clotting system, including coagulation factor X, coagulation factor IX and protein C by cleavage of Arg-|-Xaa bonds. Has no action on insulin B chain. Binds 1 zinc ion per subunit. Heterotrimer; disulfide-linked. The heterotrimer consists of 1 heavy chain and 2 light chains (lectins): LC1 and LC2. Expressed by the venom gland. N-glycosylated; probably required for conformation. Removal of easily accessible sugars does not change its functional capacity, but removal of the core sugars with N-glycanase causes a virtually complete loss of enzyme activity, apparently as a result of major conformational changes in the molecule. Not O-glycosylated. Belongs to the venom metalloproteinase (M12B) family. P-III subfamily. P-IIId sub-subfamily.