Coagulation factor IXa and coagulation factor X (FIXa/FX)

The intrinsic tenase complex is a pivotal enzymatic assembly in the coagulation cascade, responsible for the rapid activation of factor X to factor Xa. This complex is composed of the activated serine protease factor IX (FIXa), its essential non-enzymatic cofactor activated factor VIII (FVIIIa), calcium ions, and a procoagulant phospholipid membrane [1, 2]. Within this assembly, FVIIIa serves as a molecular scaffold that brings both FIXa and factor X (FX) into close proximity, orienting them to increase the catalytic efficiency of FIXa by approximately 200,000-fold [3]. In Hemophilia A, the deficiency of FVIII prevents the formation of this complex, resulting in a failure of thrombin generation and severe bleeding tendencies [4]. Modern therapeutic strategies, such as the bispecific antibody emicizumab, target the binding partners within this complex (FIXa and FX) to mimic the spatial bridging function of FVIIIa, thereby restoring the coagulation process in patients with or without FVIII inhibitors [5]. This mechanism effectively bypasses the need for FVIII, providing a stable hemostatic effect and reducing the frequency of bleeding episodes [5]. [1] StatPearls, Physiology, Coagulation Cascade, 2023. [2] UniProt, Coagulation factor IX (P00740) and Coagulation factor X (P00742). [3] Fay, P. J., Activation of factor X by the intrinsic tenase complex, Blood Reviews, 2004. [4] National Hemophilia Foundation, Hemophilia A, 2023. [5] Oldenburg, J., et al., Emicizumab Prophylaxis in Hemophilia A with Inhibitors, New England Journal of Medicine, 2017.

Other names

Intrinsic tenase complex componentsFactor VIII binding partnersFIXa and FXFactor IXa and Factor X

Bispecific antibody bridging of Factor IXa and Factor X to mimic the cofactor function of activated Factor VIII.