Contact activation of plasma: structure-activity relationships of human high molecular weight kininogen.

Human high MW kininogen can be isolated as a single polypeptide chain of 110,000 MW. Purified human plasma kallikrein cleaves this molecule to give a disulfide-linked, two chain molecule, free of kinin, that retains full clotting activity. Following reduction and carboxymethylation of the two chain molecule, a light chain can be isolated that quantitatively retains the full coagulant activity of the native molecule. During contact activation in normal human plasma a rapid cleavage of high MW kininogen along with kinin liberation occurs in a reaction that is dependent upon the presence of prekallikrein and Factor XII (Hageman factor).