Tubulin assembly induced by cobalt and zinc

Both Co(II) and Zn(II) stimulate the assembly of bovine brain 6S tubulin in the absence of organic solvents, under conditions where Mg(II) is ineffective. The products of the assembly reaction depend on the cation/tubulin ratio. At lower ratios microtubules are formed, but as the cation concentration is increased, broad sheets of protofilaments are the predominate products. The assembly reaction in Co(II) is inhibited by high ionic strength, GDP, colchicine, and Ca(II). Unlike other inhibitors, which will cause depolymerization of Co(II)-induced microtubules, Ca(II) added to Co(II)-induced microtubules causes the formation of broad sheets of protofilaments.