Factor XII is a serum glycoprotein that participates in the initiation of blood coagulation, fibrinolysis, and the generation of bradykinin and angiotensin. Prekallikrein is cleaved by factor XII to form kallikrein, which then cleaves factor XII first to alpha-factor XIIa and then trypsin cleaves it to beta-factor XIIa. Alpha-factor XIIa activates factor XI to factor XIa (By similarity). Selective cleavage of Arg-|-Ile bonds in factor VII to form factor VIIa and factor XI to form factor XIa. Interacts with HRG; the interaction, which is enhanced in the presence of zinc ions and inhibited by heparin-binding, inhibits factor XII autoactivation and contact-initiated coagulation. O- and N-glycosylated. Belongs to the peptidase S1 family. Extended N-terminus.