The binding of calcium ions to bovine factor X by rate dialysis.

The binding of Ca+2 to bovine factor X (molecular weight of 74,000) (Yue und Gertler 1977) was studied by the technique of rate dialysis and with the use of 45Ca+2. The binding data are consistent with a model of sequential mechanism. One mole of Ca+2 binds to the glycoprotein with a dissociation constant of 5.2 X 10(-5) M and additional 39 +/- 4 moles of Ca+2 bind to this zymogen with a dissociation constant of 3.7 X 10(-3) M. The binding of the high affinity Ca+2 causes a functionally significant change in the zymogen, and (calcium) (factor X) complex is the real substrate in the activation process by the protease in Russell's viper venom.