The binding of vincristine, vinblastine and colchicine to tubulin

Preparations of tubulin were examined for their ability to bind vincristine, vinblastine, and colchicine, as measured by adsorption on DEAE impregnated filter paper. Vincristine and vinblastine were found to bind very rapidly with tubulin (4 hr). When varying concentrations of the alkaloids were employed, and the data examined on a Scatchard plot, it was found that colchicine had an association constant of 1.8 × 10 6 liters/mole, while vinblastine and vincristine had constants of 6.0 × 10 6 liters/mole and 8.0 × 10 6 liters/mole respectively. In addition, it was found that the ratio of molar binding of colchicine was always twice that of vinblastine or vincristine.