Comparison of the β-tubulin sequences with the equilibrium colchicine K a and the K i for inhibition by podophyllotoxin suggests that residue β: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.
