title: Tubulin-colchicine complex (TC) inhibits microtubule depolymerization by a capping reaction exerted preferentially at the minus end.
abstract: The effects of colchicine and tubulin-colchicine complex (TC) on microtubule depolymerization were studied using the axoneme-subunit system described previously [Bergen LG, Borisy GG; J Cell Biol 84:141-150, 1980]. This system allows the independent analysis of the polymerization kinetics at both the plus and minus ends of a microtubule. Depolymerization was induced by isothermal dilution with 10 volumes of an experimental solution containing colchicine, TC, or buffer alone. Colchicine alone (5-100 microM) blocked depolymerization at the minus end, whereas depolymerization at the plus end occurred at almost control rates. A similar effect was produced by TC (0.4:1-1:1 molar ratio to free tubulin). High molar ratios of TC to tubulin (10:1) blocked depolymerization at both plus and minus ends, and intermediate molar ratios of TC:T allowed depolymerization of the plus ends but at attenuated rates. The blockage was not readily reversible; TC-affected ends neither shortened upon dilution nor grew longer upon incubation with additional tubulin. We conclude that TC at suprastoichiometric ratios to tubulin inhibits microtubule depolymerization by a capping reaction and that this effect is exerted preferentially at the minus end.
mesh_terms: D000818:Animals; D002696:Chlamydomonas / Q000648:ultrastructure; D003078:Colchicine / Q000494:pharmacology*; D005407:Flagella; D007700:Kinetics; D008854:Microscopy, Electron; D008870:Microtubules / Q000187:drug effects / Q000648:ultrastructure*; D011108:Polymers; D012996:Solutions; D013552:Swine; D014404:Tubulin / Q000494:pharmacology*
chemical_list: D011108:Polymers; D012996:Solutions; D014404:Tubulin; D003078:Colchicine