title: Guanosinetriphosphatase activity of tubulin associated with microtubule assembly.
abstract: Tubulin, purified by cycles of assembly followed by phosphocellulose chromatography, exhibits a characteristic GTPase activity that is polymerization dependent and can be attributed to the tubulin itself. This activity has been observed, in a standard reassembly buffer containing low Mg2+, under three conditions that induce microtubule assembly: in the presence of microtubule-associated proteins, in the presence of DEAE-dextran, or after addition of high Mg2+ and glycerol. The phosphocellulose-purified tubulin showed no GTPase activity under the following nonpolymerizing conditions: in buffer with low Mg2+ in the absence of microtubule-associated proteins or DEAE-dextran, in buffer with high Mg2+ and glycerol at tubulin concentrations below the critical concentration, or when microtubule assembly was inhibited by vinblastine. Colchicine, on the other hand, while blocking microtubule assembly, induced a significant GTPase activity in the phosphocellulose-purified tubulin. During the process of assembly, GTP appears to be hydrolyzed as a free tubulin dimer polymerizes into a microtubule. A constant GTPase activity when polymerization equilibrium is reached apparently reflects the cyclic polymerization-depolymerization of tubulin dimers at the ends of the microtubules.
mesh_terms: D000818:Animals; D001921:Brain / Q000201:enzymology; D002852:Chromatography, Ion Exchange; D003078:Colchicine / Q000494:pharmacology; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D006023:Glycoproteins / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism; D007700:Kinetics; D008870:Microtubules / Q000201:enzymology*; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D013552:Swine; D014404:Tubulin / Q000302:isolation & purification / Q000378:metabolism*; D014747:Vinblastine / Q000494:pharmacology
chemical_list: D006023:Glycoproteins; D014404:Tubulin; D014747:Vinblastine; D006160:Guanosine Triphosphate; D010744:Phosphoric Monoester Hydrolases; D020558:GTP Phosphohydrolases; D003078:Colchicine