The Kinin System of Human Plasma V. The Probable Derivation of Prekallikrein Activator from Activated Hageman Factor (XIIa) 1

Summary

A partially purified preparation of activated Hageman factor (factor XIIa) was prepared by anion exchange chromatography and gel filtration (Sephadex G-200) of noncontact human platelet poor plasma. The factor XIIa preparation corrected the clotting defect of congenitally factor XII-deficient plasma, but not that of plasma depleted of factor XI. It had a pI of approximately 5.3 and an approximate molecular weight of 118,000 by gel filtration and 86,000 by sucrose density gradient ultracentrifugation.

When treated with trypsin or Celite, it developed prekallikrein-activating activity. No such activity could be induced with the factor XIIa preparation. The prekallikrein activator, as described before, was highly anionic and had a molecular weight of less than 40,000. It migrated as a prealbumin by disc electrophoresis. Multiple bands were present in the factor XIIa preparation, which eluted as a β-globulin during disc electrophoresis.

Some evidence is presented that the prekallkrein activator is a fragment (XIIf) of the parent molecule (XIIa) and that the fragment loses some of the clot-promoting activity, while it acquires prekallikrein activating activity. Whereas the prekallikrein activator was susceptible to DFP, its clot-promoting activity was only partially inhibited by this serine esterase inhibitor. On the other hand, DFP in a concentration as high as 10^-3 M had no inhibitory effect on intact factor XIIa.