Activated factor X, also known as factor Xa, is an essential protein component of the blood coagulation system. It is an enzyme that plays a crucial role in the conversion of prothrombin to thrombin, an event necessary for the initiation and propagation of blood clot formation.
Factor X is primarily produced in the liver and circulates in an inactive form until it is triggered by various factors in the coagulation cascade. Upon activation, factor X undergoes a series of proteolytic cleavages, leading to the creation of activated factor X (factor Xa). This conversion occurs through the action of coagulation factors such as factor IXa and factor VIIIa, which form a complex on the surface of activated platelets or damaged endothelial cells.
Activated factor X then functions as a serine protease, cleaving prothrombin at specific sites to generate thrombin. Thrombin, in turn, mediates the cleavage of fibrinogen to fibrin, the major protein that forms the basic framework of blood clots. Additionally, factor Xa also positively regulates its own formation by amplifying the activation of factor IX to factor IXa in a positive feedback loop.
Various interactions with cofactors and inhibitors modulate the activity of activated factor X, ensuring a delicate balance in the clotting process. Regulating factor Xa activity is essential for maintaining normal hemostasis, as excessive clot formation can lead to thrombosis, while insufficient clotting predisposes individuals to bleeding disorders. Pharmacological agents targeting the activity of factor Xa, such as direct factor Xa inhibitors, have been developed for the prevention and treatment of thrombotic conditions like deep vein thrombosis, pulmonary embolism, and stroke.
