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. Interacts with SERPINA10. 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 related to peptidase S1 family vitamin K-dependent clotting factors, it has lost two of the essential catalytic residues and therefore lacks protease activity.