Factor xi

Factor XI or Plasma Thromboplastin Antecedent is one of the enzymes that participate in the blood coagulation process. It is a zymogen, an inactive precursor of an enzyme, which is activated by Factor XII (Hageman factor). The activated Factor XI (Factor XIa) in turn activates Factor IX. Deficiency of Factor XI causes a rare disorder known as Hemophilia C.

Structure

Factor XI is a dimer with each monomer composed of four apple domains and a serine protease domain. The apple domains are responsible for the activation of Factor XI and its binding to platelets.

Function

Factor XI plays a crucial role in the coagulation cascade, which is a series of reactions that lead to the formation of a blood clot. It is activated by Factor XII and, in its activated form (Factor XIa), it activates Factor IX by cleaving it. Factor IX, in turn, contributes to the formation of a blood clot.

Clinical Significance

Deficiency of Factor XI results in a mild bleeding disorder known as Hemophilia C. It is less severe than Hemophilia A and Hemophilia B. The disorder is usually discovered when a person has prolonged bleeding after surgery or trauma. Treatment involves infusions of plasma or recombinant Factor XI.

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