Effect of calcium on the polymerization of the tubulin-colchicine complex in a BES buffer

The most fundamental property of tubulin is microtubule assembly, and then the polymerization reaction is the basic in the case of the tubulin-colchicine complex. Comparing the results carried out under the different conditions is important, because microtubule formation is affected by the condition. The polymerization was observed above at a concentration of 4 and 6 mM MgCl_2 at pH 6.5 and 7.0, respectively, in a BES buffer. The increase of magnesium concentration induced the high turbidity due to the polymerization. We indicated calcium ion inhibited the polymerization at low concentration. The presence of calcium ion induced the increase of critical concentration for polymerization. We also observed, however, some tendency of acceleration of the polymerization due to a high concentration of calcium ion even in the presence of any concentration of magnesium ion. The ratio of inhibition by calcium was much more dependent on the magnesium concentration, especially the change of the inhibitory ratio was big at pH 7.0