Summary
Experiments with highly purified activated bovine Hageman factor revealed that surface activation of Hageman factor is effective only when PTA is present simultaneously. Surface activation of Hageman factor probably is not caused only by an alteration of the Hageman factor itself but by the catalyzing action of surface on the reaction between this factor and PTA, possibly by preferential adsorption of these factors. Arguments are given for the supposition that Hageman factor forms a complex with PTA which is unstable and probably identical with the so-called activation product. The instability of this activation product is caused by deterioration of PTA while Hageman factor remains. The process of contact activation stops because further Hageman factor activity is blocked by PTA which sticks to Hageman factor even after it is deteriorated. In normal circumstances not all Hageman factor molecules are adsorbed to a surface by the competing effect of other proteins in the plasma with glass affinity. Exposing plasma to a large surface such as provided by celite, causes complete adsorption of all Hageman factor molecules and in this way causes complete consumption of PTA.
