Inhibition of microtubule polymerization by micromolar concentrations of mercury (II)

Polymerization of microtubule protein in vitro has been tested in the presence of Hg2+. Inhibition occurs in the presence of Hg2+ concentrations lower than the molarity of the tubulin, even in the presence of 0.5 mM ethylenebis(oxyethylenenitrilo)tetraacetic acid. The estimated concentration of free Hg2+ under these conditions is less than 10(-20) M. The extent of inhibition is approximately stoichiometric in that the molar quantity of tubulin that fails to polymerize is comparable to or slightly greater than the total Hg2+ present as chelate. The affinity of the susceptible site for Hg2+ in microtubule protein must be exceptionally high and may not be protected by natural chelating agents in the cell. Preformed microtubules are rapidly depolymerized on addition of Hg2+ chelate. In vitro, inhibition is both prevented and rapidly reversed by 2-mercaptoethanol.