Coagulation factor IXa (FIXa) (FIXa)

Coagulation factor IXa (FIXa) is a vitamin K-dependent serine protease that plays a central role in the intrinsic pathway of the blood coagulation cascade (UniProt P00740). It is generated from its zymogen, Factor IX, by the proteolytic action of either Factor XIa or the Factor VIIa/tissue factor complex. Once activated, FIXa associates with its cofactor, Factor VIIIa, on a phospholipid surface to form the intrinsic tenase complex, which efficiently activates Factor X to Factor Xa (PubMed: 21815710). This step is a critical amplification point in the production of thrombin, making FIXa an attractive therapeutic target for anticoagulants aimed at preventing or treating thromboembolic diseases such as deep vein thrombosis and stroke (PubMed: 15507607). The Antithrombin-Factor IXa (AT-FIXa) complex is the physiologically inactive form of the enzyme, created when the circulating inhibitor antithrombin neutralizes FIXa. Measurement of the AT-FIXa complex serves as a sensitive clinical biomarker for the activation of the coagulation system and the efficacy of drugs that modulate this pathway (PubMed: 8504241). Drugs targeting this system include indirect inhibitors like heparin, which accelerate the formation of the AT-FIXa complex, and direct inhibitors like the RNA aptamer pegnivacogin.

Other names

Activated coagulation factor IXActivated Christmas factorFactor IXa-antithrombin complexFIXa-AT complexFactor IXa – ATIII–Factor IXa complex

Inhibition of the catalytic activity of Factor IXa or acceleration of its neutralization by antithrombin to prevent the formation of the tenase complex and subsequent thrombin generation (PubMed: 15507607).