title: Interaction of tubulin with single ring analogues of colchicine.
abstract: Simple analogues of the tropolone and trimethoxyphenyl moieties of colchicine have been used as probes for the colchicine binding site of purified calf brain tubulin. [3H]Tropolone methyl ether was found to bind to one site per tubulin molecule with equilibrium constant of (2.2 +/- 0.2) x 10(3) M-1 at 0 degree C, with the interaction having delta H0app = -8.3 +/- 1.0 kcal mol-1 and delta S0app = -15.2 +/- 3.6 eu. The binding of tropolone methyl ether and colchicine was inhibited by each other. Both tropolone and its methyl ether inhibited tubulin polymerization into microtubules in vitro. N-[3H]Acetylmescaline bound to tubulin with a K congruent to 4 x 10(2) M-1 at 37 degrees C. This interaction was inhibited by colchicine and at lower temperatures was below the sensitivity of the measuring method employed. [14C]Mescaline interacted with higher affinity site(s) not related to the colchicine site. Both mescaline and N-acetylmescaline inhibited partially the microtubule assembly at 10(-3) M concentrations. No linkage was observed between the binding of tropolone methyl ether and N-acetylmescaline. The relatively weak interactions of both the two separate parts of colchicine can account quantitatively for the much tighter binding of the complete drug to tubulin within a proposed model which takes into account the entropic advantage of colchicine as a bifunctional ligand.
mesh_terms: D003078:Colchicine / Q000031:analogs & derivatives*; D007700:Kinetics; D011485:Protein Binding; D013329:Structure-Activity Relationship; D013816:Thermodynamics; D014404:Tubulin
chemical_list: D014404:Tubulin; D003078:Colchicine