Interaction of Ni2+ with the tubulin-microtubule system

In vitro polymerization of purified goat brain tubulin is stimulated at low Ni2+ concentration, whereas at high nickel concentration (greater than 1 . 10(-4)) polymerization is inhibited. Ni2+, over the concentration range of 1 . 10(-4)-1 . 10(-3) M, enhances the rate of colchicine binding to tubulin, although in its presence the colchicine binding site of tubulin is degraded at a much faster rate at 37 degrees C. Finally, incubation of tubulin with Ni2+ at 37 degrees C gradually alters the native conformation of the protein, as revealed by the quenching of intrinsic tryptophan fluorescence.