Interaction of colchicine analogues with purified tubulin

Binding of two colchicine analogues, desacetamidocolchicine and 2-methoxy-5-(2′,3′,4′-trimethoxyphenyl) tropone to purified tubulin have been studied. Both analogues bind to tubulin with a significant increase in fluorescence polarization of the drugs in solutions containing tubulin. The K_d for tubulin-drug complexes were found to be 1.25 × 10^-6 M and 1.08 × 10^-6 M for desacetamidocolchicine and 2-methoxy-5-(2′,3′,4′-trimethoxyphenyl) tropone, respectively. Scatchard analysis of the fluorescence titration curve of drug tubulin interaction also gives the values of stoichiometry and affinity constant. These were 0.8 and 1.6 × 10⁶ M^-1 for desacetamidocolchicine, and 0.9 and 0.58 × 10⁶ M^-1 for 2-methoxy-5-(2′,3′,4′-trimethoxyphenyl) tropone.