Stable blood coagulation factor activated by contact with the subendothelial surface of an injured vessel. Along with prekallikrein, it serves as the contact factor that initiates the intrinsic pathway of blood coagulation. Kallikrein activates factor XII to XIIa. Deficiency of factor XII, also called the Hageman trait, leads to increased incidence of thromboembolic disease. Mutations in the gene for factor XII that appear to increase factor XII amidolytic activity are associated with HEREDITARY ANGIOEDEMA TYPE III.
Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D015956
Factor XIIa
Activated form of factor XII. In the initial event in the intrinsic pathway of blood coagulation, kallikrein (with cofactor HIGH MOLECULAR WEIGHT KININOGEN) cleaves factor XII to XIIa. Factor XIIa is then further cleaved by kallikrein, plasmin, and trypsin to yield smaller factor XII fragments (Hageman-Factor fragments). These fragments increase the activity of prekallikrein to kallikrein but decrease the procoagulant activity of factor XII.