Analysis of the colchicine-binding site of beta-tubulin.

Comparison of the beta-tubulin sequences with the equilibrium colchicine Ka and the Ki for inhibition by podophyllotoxin suggests that residue beta:316 is directly involved in binding the common trimethoxyphenyl-(or A-) ring. By contrast, the analysis indicates that the local hydrophobicity affects the rate of one of the two conformational changes associated with colchicine binding but does not determine the affinity of the colchicine-binding site.