Factor XIII is activated by thrombin and calcium ion to a transglutaminase that catalyzes the formation of gamma-glutamyl- epsilon-lysine cross-links between fibrin chains, thus stabilizing the fibrin clot. Also cross-link alpha-2-plasmin inhibitor, or fibronectin, to the alpha chains of fibrin. Defects in F13A1 are the cause of factor XIII subunit A deficiency (FA13AD). FA13AD is an autosomal recessive disorder characterized by a life-long bleeding tendency, impaired wound healing and spontaneous abortion in affected women. Belongs to the transglutaminase superfamily. Transglutaminase family. Note: This description may include information from UniProtKB.