Factor XII (F XII, Hageman factor) is a 80 kDa, single chain glycoprotein that circulates in blood as an inactive zymogen. F XII plays an important role in blood coagulation, fibrinolysis, and kinin generation. Factor XII is activated by kallikrein in alpha-factor XIIa, which is further converted by trypsin into beta-factor XIIa. Alpha-factor XIIa is composed of a 52 kDa NH2-terminal heavy chain, called coagulation factor XIIa heavy chain, and a 28 kDa COOH-terminal light chain, called coagulation factor XIIa light chain, connected by a disulfide bond. Beta-factor XIIa is composed of 2 chains linked by a disulfide bond, an N-terminal nonapeptide, called beta-factor XIIa part 1, and coagulation factor XIIa light chain, also known in this context as beta-factor XIIa part 2.