The accelerating effect of bovine plasma HMW kininogen on the surface-mediated activation of factor XII: generation of a derivative form (active kininogen) with maximal cofactor activity by limited proteolysis.

Abstract

<h2>Abstract</h2> The accelerating effect of HMW kininogen in the kaolin-mediated activation of bovine Factor XII was markedly enhanced after the brief treatment with urinary kallikrein or plasma kallikrein (but not with plasmin). At the early stage of the incubation, the cleavage of a single chain HMW kininogen and the enhancement of the accelerating effect preceded the kinin liberation, indicating that a nicked form of HMW kininogen is more active as a cofactor than the intact form. Thus, in the initial phase of intrinsic blood coagulation, plasma kallikrein seems to play an important role not only in the activation of Factor XII but also in the transformation of HMW kininogen to a nicked form with higher cofactor activity, an "active kininogen".