The contact phase of blood coagulation: clotting factors XI and XII, their isolation and interaction

The blood clotting factor XII has been obtained in highly purified and factor XI in a partially purified form by anion exchange chromatography on QAE-Sephadex, gel filtration on Sephadex G-200, and cation exchange chromatography on CM-Sephadex and SP-Sephadex. To obtain a preparation of factor XII that was homogeneous by disc gel electrophoresis it was further purified by absorption to celite and, after washing, it was desorbed with 1.0 M NaCl and rechromatographed on QAE Sephadex. Factor XII is a 4.9 to 5.0 S, β-globulin with an isoelectric point of about 6.3, a diffusion coefficient of 4.8 to 4.9, and an estimated molecular weight of 92,000 (115,000 by gel filtration). Factor XI is a 7.4 S protein, migrating as a γ-globulin; its pI is 7.8 to 8.6, peaking at 8.0 to 8.2, and its diffusion coefficient is about 3.4. Its estimated molecular weight is about 170,000 to 1 80,000. A mixture of activated factor XII (XIIa) and highly fragmented XII (XIIf, prekallikrein activator) can convert factor XI to XIa. Conversion of factor XI to its activated form can be induced also with a highly purified preparation of XIIf. The rate and magnitude at which the development of clot-promoting activity, i.e., conversion of XI to XIa occurs, depends on the concentration of factor XIIa XIIf, whereas the magnitude of the clot-promoting activity which develops, is primarily a function of the concentration of factor XI, suggesting an enzymatic mechanism. These findings confirm those of other investigators, using crude fractions. 7 , 31 Monospecific antibody against factor XII inhibits the clot-promoting activity of this factor. The same is true of antibody directed against factor XI. Antibody against one clotting factor does not inhibit the clot-promoting activity of the other clotting factor and vice versa.