Factor XII

Literature References: Mol wt about 82,000. An enzyme which circulates in zymogen form in blood and when activated initiates the first of a series of events in coagulation of blood plasma. Enzymatic nature of blood coagulation is described by the "cascade" theory in which clotting factors interact with one another in a stepwise manner, one acting as an enzyme, the other as substrate, in a sequence of reactions leading to the formation of thrombin, q.v.: Davie, Ratnoff, Science 145, 1310 (1964); MacFarlane, Nature 202, 498 (1964). Factor XII initiates clotting when blood or plasma comes into contact with glass, collagen, or surface-active agents. Once activated, it interacts with factor XI, q.v., to convert it to an enzyme. Factor XII is a sialoglycoprotein with esterase activity. Its activation by glass may be viewed as a dynamic alteration of the tertiary structure of the protein moiety: Schoenmakers et al., Biochim. Biophys. Acta 101, 166 (1965). Isoln of human and rabbit factor XII in zymogen form: C. G. Cochrane, K. D. Wuepper, J. Exp. Med. 134, 986 (1971); H. Saito et al., Circ. Res. 34, 641 (1974). Highly purified Hageman factor undergoes a change in physical properties during activation: Donaldson, Ratnoff, Science 150, 754 (1965). Factor XII deficiency is termed the Hageman trait. Unlike deficiencies in all other clotting factors, persons with Hageman trait do not show significant bleeding tendencies. Reviews: Ratnoff in New Blood Clotting Factors, I. S. Wright et al., Eds. (Schattauer-Verlag, Stuttgart, 1960) pp 116-122; Ratnoff et al., in Thrombolytic Activity and Related Phenomena, I. S. Wright et al., Eds. (Schattauer-Verlag, Stuttgart, 1961) pp 364-378; several authors in Recent Advances in Blood Coagulation, L. Poller, Ed. (J. & A. Churchill, London, 1969); J. Spragg, K. F. Austen, Compr. Immunol. 3, 125-143 (1977); J. H. Griffin, C. G. Cochrane, Methods Enzymol. 45B, 56-65 (1976).