Coagulation factors II, IX, X (FII, FIX, FX)

Coagulation factors II (prothrombin), IX, and X are essential vitamin K-dependent serine proteases in the blood coagulation cascade. Factor II (prothrombin) is cleaved to form thrombin (factor IIa), which plays a pivotal role in converting fibrinogen to fibrin and activating additional coagulation factors[3][4]. Factor IX is a key enzyme of the intrinsic pathway; when activated (FIXa), it complexes with factor VIIIa to convert factor X to Xa[1][3][4][7]. Factor X, once activated (FXa), forms part of the prothrombinase complex, catalyzing prothrombin activation to thrombin, leading to fibrin clot formation[3][4]. They are structurally characterized by an N-terminal Gla domain, two epidermal growth factor-like domains, and a serine protease domain (prothrombin includes kringle domains instead of EGF-like domains)[3]. These factors are primary targets for multiple classes of anticoagulants and are critical both as diagnostic markers and as therapeutic agents in bleeding and clotting disorders.

Other names

Prothrombin (factor II)Christmas factor (factor IX)Stuart-Prower factor (factor X)Vitamin K-dependent coagulation factors

Inhibition of factor activity (e.g., direct inhibition of FXa or thrombin; vitamin K antagonism), replacement therapy, reversal of anticoagulation