FXII is a member of the contact activation proteins. It is an activator of both the coagulation and kinin systems. FXII circulates as an inactive zymogen that can be converted to FXIIa, a serine protease, either by autoactivation through contact with negatively charged surfaces or proteolytic cleavage by kallikrein. FXIIa can activate Prekallikrein and FXI. In vitro it participates in the intrinsic pathway of coagulation. The slide show entitled Coagulation Pathways (All Components) shows how FXII relates to the other coagulation factors. See also the slide show entitled Intrinsic Pathway-APTT.
