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-M(r) kininogen and factor XII/factor XIIa to phospholipids coated on to polystyrene microtiter plates was investigated by ELISA. Both high-M(r) kininogen and factor XII/factor XIIa bound specifically to the phospholipid surface. Binding was observed to negatively charged phospholipids only. The binding of high-M(r) kininogen was not affected by the presence of zinc ions. At a surface concentration of 20% phosphatidylinositol phosphate in phosphatidylcholine a dissociation constant (k(D)) of 10 nM for the binding of high-M(r) kininogen was calculated. The amount of bound purified alpha-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 alpha-factor XIIa was inhibited by high-M(r) kininogen. Independent of the presence of zinc ions or high-M(r) kininogen, a k(D) of 7.9 nM was calculated for alpha-factor XIIa binding. The binding of prekallikrein was dependent upon the presence and the concentration of high-M(r) kininogen. In plasma containing aprotinin, the binding of high-M(r) 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-M(r) kininogen was probably due to the increased binding of factor XII, which displaced high-M(r) kininogen.