Factor Xa is a vitamin K-dependent glycoprotein that converts prothrombin to thrombin in the presence of factor Va, calcium and phospholipid during blood clotting. Selective cleavage of Arg-|-Thr and then Arg-|-Ile bonds in prothrombin to form thrombin. Heterodimer of a light chain and a heavy chain; disulfide-linked. Plasma; synthesized in the liver. Gamma-carboxyglutamate residues are formed by vitamin K dependent carboxylation. These residues are essential for the binding of calcium. The activation peptide is cleaved by factor IXa (in the intrinsic pathway), or by factor VIIa (in the extrinsic pathway). The iron and 2-oxoglutarate dependent 3-hydroxylation of aspartate and asparagine is (R) stereospecific within EGF domains. Belongs to the peptidase S1 family. Factor X entry