FXIII (fibrin-stabilizing factor) is a heterotetramer (consists of 2 alpha and 2 beta subunits) that circulates in blood in association with Fibrinogen. In the presence of fibrin, Thrombin converts the FXIII proenzyme to FXIIIa, the active transglutaminase. FXIIIa catalyzes the formation of intermolecular (e(g-glutamyl) lysyl) bonds between various substrates such as fibrin monomers, a2-plasmin inhibitor, fibronectin, and collagen. Accordingly FXIII is involved in hemostasis, wound healing, and maintenance of pregnancy. The slide show entitled Fibrinolytic Pathway shows how FXIII relates to the other coagulation factors.
