Description:
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.