Factor XI triggers the middle phase of the intrinsic pathway of blood coagulation by activating factor IX.
Isoform 2 is produced by platelets and megakaryocytes but absent from other blood cells.
Involvement in disease
Defects in F11 are the cause of factor XI deficiency (FA11D) [MIM:612416]; also known as plasma thromboplastin antecedent deficiency or Rosenthal syndrome. It is a hemorrhagic disease characterized by reduced levels and activity of factor XI resulting in moderate bleeding symptoms, usually occurring after trauma or surgery. Patients usually do not present spontaneous bleeding but women can present with menorrhagia. Hemorrhages are usually moderate.
Belongs to the peptidase S1 family. Plasma kallikrein subfamily. Contains 4 apple domains. Contains 1 peptidase S1 domain.
Activated by factor XIIa (or XII), which cleaves each polypeptide after Arg-387 into the light chain, which contains the active site, and the heavy chain, which associates with high molecular weight (HMW) kininogen.