Enhancement of tubulin polymerization by Cl−-induced blockade of intrinsic GTPase

► Tubulin polymerization (TP) was higher in Cl− solutions than that in Br- or NO3-. ► GTPase activity of tubulin was lower in Cl− solutions than that in Br−/NO3- solutions. ► Efficiency of TP with a non-hydrolyzable GTP (GpCpp) was higher than with GTP. ► Replacement of GTP with GpCpp on TP was more effective in Br− or NO3- than Cl−. ► Effects of Cl− on TP are partly mediated via inhibitory effects on GTPase of tubulin.