Interaction between factor XII (Hageman factor), high molecular weight kininogen and prekallikrein

Adsorption of factor XII and plasma kallikrein onto kaolin induces activation of factor XII. Trace amounts of high molecular weight (HMW)-kininogen markedly enhances the rate and the amount of activation of factor XII. Activation of factor XII was measured by its capacity to convert prekallikrein to kallikrein. This potentiating effect is dependent on the amount of HMW-kininogen. Low molecular weight kininogen has no enhancing effect. When the reactants are adsorbed to kaolin and the latter separated by centrifugation the prekallikrein-converting activity is detectable only in the kaolin-containing precipitates. Less activation of factor XII occurs when the HMW-kininogen is added not initially to the kaolin-factor XII mixture, but to the prekallikrein, indicating that the HMW-kininogen probably acts when factor XII is being activated, rather than at a later stage. Treatment of HMW-kininogen with excess trypsin, plasmin or kallikrein abolishes its potentiating effect. When HMW-kininogen is treated with increasing concentrations of kallikrein there is an inverse relationship between the generated kinin and the ability of the kininogen to enhance the activation of factor XII.