INFLUENCE OF METAL-IONS IN ACTIVATION OF BOVINE FACTOR-IX BY COAGULANT PROTEIN OF RUSSELLS VIPER VENOM

The capacity of various metal ions to support activation of bovine factor IX, by the coagulant protein of Russell's Viper venom, has been examined. The following metal ions, at concentrations which saturate their effect, promoted activation of factor IX, at approximately equal efficiency: Ca2+, Mn2+, Sr2+, and Co2+, Other metal ions, i.e., Ba2+, and Mg2+, at saturating concentrations, led to a maximum rate of activation of factor IX of 25%, compared to Ca2+, The lanthanides, Gd2+, and Tb3+, also promoted activation in this system, at maximal rates of approximately 15%, compared to Ca2+, In this study, it was also discovered that the esterase activity of bovine factor IXa was dependent upon the presence of metal ions. Utilizing α-N-benzoyl-l-arginine ethyl ester as the substrate, steady state kinetic analysis in the absence of metal ion indicated that the Km and Vmax for this substrate was 20 mm and 2.9 μmol substrate cleaved min-1 mg-1 of factor IXa, respectively, at pH 8.0 and 30 °C. In the presence of optimal concentrations of Ca2+, Mn2+, Mg2+, Sr2+, and Ba2+, the Vmax values for this same substrate increased to 6.7, 5.9, 5.0, 5.0, and 3.7 μmol cleaved min-1 mg-1 of factor IXa, respectively. None of these metal ions had an affect on the Km value of this substrate. © 1978.