Colchicine, bioactivity

In looking at these conclusions, one could speculate that rings A and C in these spindle toxins are most important, and they may bind to different loci on the colchicine binding site. It is suspected that two sites of tubulin which respectively bind to rings A and C of colchicine and its bioactive analogs are part of a polypeptide segment which is arranged in a helix, as shown in Fig. 28. 

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