Kininogen (Kininogen)
or Fitzgerald factor or Cardiac
HMW Kininogen is part of the intrinsic pathway of coagulation, together with Factor XII (Hageman factor) and prekallikrein. It is 626 amino acids long, and MW 88 to 120 kD (dependent on glycosylation). Kininogen HMW is not enzymatically active, and only functions as a cofactor for the activation of kallikrein and Hageman factor. It is also necessary for the activation of factor XI by factor XIIa.
HMW Kininogen is also a precursor of bradykinin; released through positive feedback by kallikrein.
As an endogenous protein substrate for tissue kallikrein, LMW Kininogen is involved in blood pressure regulation. Proteolytic cleavage by kallikrein releases vasoactive bradykinin from LMW kininogen. In addition, LMW kininogen, like HMW kininogen, is a major extracellular cysteine proteinase inhibitor.