Factor x

Factor X is a serine protease (enzyme) that plays a critical role in the coagulation cascade, which is the series of reactions that ultimately leads to the formation of a blood clot. It is also known as Stuart-Prower factor, named after the two patients in whom the factor was first identified. Factor X is synthesized in the liver and requires vitamin K for its production.

Structure

Factor X is a single-chain glycoprotein that is composed of two domains: a light chain and a heavy chain. The light chain contains a Gla domain (gamma-carboxyglutamic acid), which is responsible for the vitamin K-dependent carboxylation of certain glutamate residues. The heavy chain contains the serine protease domain.

Function

Factor X is activated (to factor Xa) by both the intrinsic and extrinsic pathways of the coagulation cascade. The intrinsic pathway is initiated when blood comes into contact with negatively charged surfaces, while the extrinsic pathway is initiated by tissue damage. Once activated, factor Xa converts prothrombin to thrombin, which then converts fibrinogen to fibrin, the main component of a blood clot.

Clinical significance

Deficiency of factor X is a rare condition that can lead to increased bleeding. It can be inherited (congenital) or acquired, for example, due to liver disease or vitamin K deficiency. Treatment typically involves replacement therapy with factor X concentrate.

Factor Xa is also a target for anticoagulant drugs, such as rivaroxaban and apixaban, which are used to prevent and treat conditions like deep vein thrombosis and pulmonary embolism.

See also

• Coagulation
• Vitamin K
• Blood clot
• Rivaroxaban
• Apixaban