Binding of colchicine to renal tubulin at 5 degrees C

Previous reports in the literature state that the binding of colchicine to soluble tubulin is negligible at 0 - 4 degrees C as measured by non-equilibrium binding methods. In contrast, we have detected significant binding of colchicine to tubulin at 5 degrees C. Furthermore, for the first time equilibrium dialysis has been used to measure colchicine binding. The value of the dissociation constant was 1.8 microM at 5 degrees C, and the stoichiometry of colchicine binding at 5 degrees C equaled that at 37 degrees C. Dissociation at 5 degrees C of bound colchicine was negligible over a period of 23 h, and the estimated minimal half-time of dissociation was 150 h.