Appears to assist hemostasis by binding thrombin and promoting its association with phospholipid vesicles. Inhibits activity of the coagulation protease factor Xa in the presence of SERPINA10, calcium and phospholipids (By similarity). Plasma. The iron and 2-oxoglutarate dependent 3-hydroxylation of aspartate and asparagine is (R) stereospecific within EGF domains. Belongs to the peptidase S1 family. Although homologous with the vitamin K-dependent clotting factors, it has lost two of the essential catalytic residues and has no enzymatic activity.