Coagulation Factor XI (F11)

Factor XI is the zymogen form of factor XIa, one of the enzymes of the coagulation cascade. Like many other coagulation factors, it is a serine protease.Factor XI (FXI) is produced by the liver and circulates as a homo-dimer in its inactive form. The plasma half-life of FXI is approximately 52 hours.

The zymogen factor is activated into factor XIa by factor XIIa (FXIIa), thrombin, and it is also autocatalytic, and FXI is a member of the "contact pathway" due to activation by FXIIa (with includes HMWK, prekallikrein, factor XII, factor XI and factor IX).Factor XIa activates factor IX by selectively cleaving arg-ala and arg-val peptide bonds. Factor IXa, in turn, activates factor X.Inhibitors of factor XIa include protein Z-dependent protease inhibitor (ZPI), which is independent of protein Z.