Coagulation factor X (activated as serine protease factor Xa) (Factor Xa)

Factor Xa is the *activated form* of blood coagulation factor X, a serine protease critical for the formation of thrombin in the coagulation cascade[1][3][5]. Synthesized in the liver as a vitamin K-dependent zymogen (inactive precursor), factor X is activated by proteolytic cleavage via either the intrinsic (factors IXa and VIIIa) or extrinsic pathway (factor VIIa and tissue factor), yielding factor Xa[1][2][3][5]. Factor Xa, in complex with factor Va on phospholipid surfaces (especially activated platelets), forms the prothrombinase complex, converting prothrombin to thrombin with high efficiency[1][3][6]. Its enzymatic activity relies on a conserved catalytic triad (His, Asp, Ser)[5], with substrate specificity for Arg residues[4][5]. Beyond clotting, factor Xa participates in cell signaling by activating protease-activated receptors (PAR-1, PAR-2)[3], mediating cellular responses in inflammation, tissue remodeling, and tumor biology[1][3]. Factor Xa is the target of several modern anticoagulant drugs, with inhibition presenting both significant therapeutic utility for thrombosis and associated bleeding risks[1][3]. Deficiency or excessive inhibition leads to hemorrhagic complications, while excessive activity promotes thrombotic states[1][2][3]. Factor Xa is encoded by the F10 gene on chromosome 13q34 and is subject to regulation by vitamin K and protein Z-dependent inhibitors[1][2]. Its structure and active site have been extensively characterized in complexes with small molecule inhibitors[1][2][7].

Other names

Stuart factorBlood coagulation factor XF10 (gene symbol)Activated factor XFXa

Direct inhibition of active site (competitive binding, e.g. rivaroxaban, apixaban) Indirect reduction of synthesis (warfarin, vitamin K antagonism) Stabilization or mimicry of interaction with regulatory elements (fondaparinux)