title: Association of thiocolchicine with tubulin.
abstract: Thiocolchicine, a colchicine analog in which the C-10 methoxy is replaced with a thiomethyl moiety, was shown to bind with high affinity to the colchicine site on tubulin (Ka = 1.07 +/- 0.14 x 10(6) M-1 at 23 degrees C). Like colchicine, the association kinetics were biphasic, and the rate constants of both phases were temperature dependent. The rate constant of the fast phase of the association was 4 times greater than the rate constant for colchicine binding, and the activation energy was lower (19.1 +/- 1.8 kcal/mol). X-ray crystallographic analysis shows that thiocolchicine displays greater puckering of the tropone C ring than colchicine (Koerntgen, C. and Margulis, T. N. (1977) J. Pharm. Sci. 66, 1127-1131.). These results indicate that the conformation of the C ring may have little effect on the energetics of colchicinoids binding to tubulin.
authors.affiliation: Department of Chemistry, State University of New York, Binghamton 13901.
authors.forename: R M
authors.initials: RM
authors.lastname: Chabin
authors.forename: S B
authors.initials: SB
authors.lastname: Hastie
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002417:Cattle; D003078:Colchicine / Q000031:analogs & derivatives* / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D011485:Protein Binding; D013050:Spectrometry, Fluorescence; D013329:Structure-Activity Relationship; D013696:Temperature; D014404:Tubulin / Q000378:metabolism*
chemical_list: D014404:Tubulin; C014856:thiocholchicine; D003078:Colchicine