The binding of bovine factor XII to kaolin.

Purified bovine factor XII was radiolabeled with iodine-125 and its binding to kaolin studied. Binding was rapid and was not readily reversible upon adding unlabeled factor XII. The optimum pH for binding was in the region of pH 5-7. The isoelectric point of factor XII was pH 5.7. High concentrations of urea or increasing the ionic strength of the medium did not inhibit binding. Polyvalent macromolecules, such as Polybrene and polylysine, were effective inhibitors of factor XII binding to kaolin. Polylysine caused the release of factor XII that had bound to the kaolin surface.