Biochemistry
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Vinca site agents are antimicrotubule compounds that bind to the same site on tubulin as do the vinca alkaloids. These include agents that induce the formation of nonmicrotubule oligomers of tubulin (vinblastine and vincristine) and agents that do not (maytansine and rhizoxin). All of these quench the fluorescence of tubulin upon binding. ⋯ The vinca alkaloids differ from maytansine and rhizoxin by causing a large enhancement of chymotryptic cleavage of beta and a large inhibition of typtic cleavage of alpha, after Arg-339. These effects are interpreted as due to vinca induced oligomerization of tubulin. It is argued that the common binding site for the vinca site agents is located on beta-tubulin, close to the helix that is disrupted by colchicine.