Snake venom activators of factor X: an overview.

Activators of blood coagulation factor X have been described in the venom of many snake species belonging to the genus Viperidae and Crotalidae as well as from a few Elapid species. Based on the structural and functional properties of purified activating principles, factor X activators are either metalloproteases or serine proteases. The best known activator is RVV-X from Russell's viper (Daboia russelli), a metalloprotease consisting of a heavy chain containing the catalytic domain and two light chains which share homology with C-type lectins and which are thought to exert a regulatory function in the Ca(2+)-dependent activation of factor X. This activator is also one of the best examples of the use of exogenous activators in coagulation research and in addition it is used in many diagnostic research kits. In this paper, an overview is given of the structural and functional properties of snake venom factor X activators thus far described in the literature.