Zinc ions promote the binding of factor XII/factor XIIA to acidic phospholipids but have no effect on the binding of high‐Mr kininogen

Binding of high-Mr kininogen and factor XII/factor XIIa to phospholipids coated on to polystyrene microtiter plates was investigated by ELISA. Both high-Mr kininogen and factor XII/factor XIIa bound specifically to the phospholipid surface. Binding was observed to negatively charged phospholipids only. The binding of high-Mr kininogen was not affected by the presence of zinc ions. At a surface concentration of 20% phosphatidylinositol phosphate in phosphatidylcholine a dissociation constant (kD) of 10 nM for the binding of high-Mr kininogen was calculated. The amount of bound purified α-factor XIIa could be increased 4–5-fold in the presence of zinc ions. The lowest zinc ion concentration giving maximal binding was 0.1 mM. The binding of α-factor XIIa was inhibited by high-Mr kininogen. Independent of the presence of zinc ions or high-Mr kininogen, a kD of 7.9 nM was calculated for α-factor XIIa binding. The binding of prekallikrein was dependent upon the presence and the concentration of high-Mr kininogen. In plasma containing aprotinin, the binding of high-Mr kininogen was apparently inhibited in the presence of zinc ions, which was a prerequisite for the binding of factor XII. This apparently inhibitory effect of zinc ions on the binding of high-Mr kininogen was probably due to the increased binding of factor XII, which displaced high-Mr kininogen.