Coagulation factor IXa – coagulation factor VIIIa complex (FIXa-FVIIIa complex)

The activated factor IX (FIXa) – intrinsic tenase complex cofactor interaction is a pivotal step in the blood coagulation cascade (StatPearls, 2023). This complex, known as the intrinsic tenase, consists of the serine protease FIXa and its essential non-enzymatic cofactor, activated factor VIII (FVIIIa), assembled on a procoagulant phospholipid surface in the presence of calcium ions (PubMed, PMID: 29078241). Its primary biological function is to catalyze the conversion of factor X to factor Xa, a process that is several orders of magnitude more efficient when the FIXa-FVIIIa complex is intact compared to FIXa alone (UniProt, P00740). Dysregulation or deficiency of the components of this interaction leads to significant pathology; a lack of FVIII or FIX results in Hemophilia A and B, respectively, characterized by life-threatening bleeding (NIH, 2022). Conversely, overactivity of the complex is associated with an increased risk of thrombosis. Modern therapeutic interventions, such as the bispecific antibody emicizumab, specifically target this interaction by mimicking the spatial orientation provided by FVIIIa to bridge FIXa and factor X, thereby restoring hemostatic function in patients with Hemophilia A (FDA, 2017).

Other names

Intrinsic tenase complexFIXa-FVIIIa interactionFactor IXa-Factor VIIIa complexTenase complex

Bispecific antibody bridging of FIXa and FX to mimic FVIIIa cofactor function; replacement of deficient coagulation factors to restore complex formation.