Calcium-dependent prothrombin (F2) activator. This protein may activate prothrombin via recognition by the regulatory subunit of the calcium ion bound conformation of its gamma-carboxyglutamic acid (GLA) domain, and the subsequent conversion of prothrombin to active thrombin is catalyzed by the catalytic subunit. Binds 1 zinc ion per subunit. Heterodimer of a metalloproteinase subunit and a regulatory subunit comprising two disulfide-linked lectins (14 kDa and 17 kDa chains) (AC Q9PRP7 and AC Q9PRP8). Expressed by the venom gland. Used for quantification of normal prothrombin (CA-1 method). Belongs to the venom metalloproteinase (M12B) family. P-III subfamily. P-IIId sub-subfamily.