Prekallikrein activation by Hageman factor: potentiation by proteins in the absence of high molecular weight kininogen.

Proteins which potentiate the conversion of prekallikrein to kallikrein by Hageman factor fragments are present in cryoprecipitate prepared from the plasma of an individual lacking HMW kininogen as well as in purified von Willebrand's factor preparations. However, the potentiator activity could be separated from the von Willebrand's antigen and ristocetin cofactor activity by chromatography on QAE-Sephadex. Moreover, it was present in plasma from an individual lacking von Willebrand's factor. These observations indicate that von Willebrand's factor is not responsible for the potentiator activity in cryoprecipitate.