Mono- and divalent cationic parameters of foot-and-mouth disease virus replicase.

Replicase induced by foot-and-mouth disease virus has an absolute requirement for Mg2+ that cannot be replaced by other divalent cations. Mn2+ and Ca2+ are effective non-competitive inhibitors. At low ionic strength, Mg2+ directly influence the V of the reaction. High ionic strength (0.2 M KCl), produces a shift in the optimum Mg2+ concentration toward lower values which enhances the V and Km. KCl is more active in stimulating activity than NaCl, LiCl or CsCl but similar to NH4Cl. (NH4)2SO4, however, is less stimulatory than the chloride salt. K+ appear to interact specifically with replicase so as to affect initiation: once the reaction has been initiated it becomes refractory to the addition of K+ and shows typical plateau kinetics under all conditions.