Alkaline earth metals are not required for the restoration of the apoform of anthrax lethal factor to its holoenzyme state

► Anthrax lethal factor houses at least one inhibitory low-affinity calcium site. ► Lethal factor binds zinc with picomolar affinity. ► The LF apoprotein can be reactivated by zinc and cobalt. ► The apoprotein does not rely on calcium of magnesium for reactivation. ► The apoprotein prepared by dialysis tends to be contaminated with chelators.