Accelerating Effect of Zinc Ions on the Surface-Mediated Activation of Factor XII and Prekallikrein12

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Abstract
The effect of zinc ions on the surface-mediated activation of factor XII and prekallikrein was studied, using the contact system reconstituted with the purified proteins from bovine and human plasmas. The sulfatide-mediated activation of factor XII and prekallikrein in the presence of high-molecular-weight (HMW) kininogen was remarkably accelerated by 10−5 M zinc ions. This accelerating effect was observed only in the presence of HMW kininogen. The kinetic analysis of the accelerating effect of zinc ions demonstrated that zinc ions reduce the Km values and increase the Vmax values on the activation of factor XII by kallikrein and on the activation of prekallikrein by factor XIIa. The value of Vmax/Km increased 26.4-fold in the former reaction and 2.8-fold in the latter reaction, indicating that zinc ions accelerate mainly the activation of factor XII by kallikrein. In the presence of 5 × 10−4 M zinc ions, typical difference spectra due to a red shift of tryptophan and/or tyrosine residues were observed for HMW kininogen and its derivatives but not low-molecular-weight (LMW) kininogen. Since the concentration of zinc ions required to induce the difference spectra is comparable with that to enhance the activation of factor XII and prekallikrein, it appears that there is some correlation between the conformational change of HMW kininogen and the enhancement of the activation.