Factor XI

Factor XI or Plasma Thromboplastin Antecedent is the zymogen form of Factor XIa, one of the enzymes of the coagulation cascade. It is part of the contact activation pathway and has an important role in both intrinsic and extrinsic coagulation pathways.

Structure

Factor XI is a dimer and each monomer is a polypeptide chain. The monomers are identical, each having a molecular weight of approximately 80,000. The chain is organized into 4 apple domains and a serine protease domain.

Function

Factor XI is activated by Factor XIIa and/or Factor IX, in a calcium-dependent manner, to Factor XIa. Factor XIa then activates Factor IX to Factor IXa, in the presence of calcium. This is the first step of the intrinsic pathway of coagulation.

Clinical significance

Deficiency of Factor XI causes the rare Hemophilia C. It is less severe than Hemophilia A and Hemophilia B. Patients with Factor XI deficiency have a normal PT (Prothrombin Time) and aPTT (Activated Partial Thromboplastin Time) may or may not be prolonged.

See also

• Coagulation
• Hemophilia
• Factor XI Deficiency

External links

• Factor XI at WikiMD

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