Dolastatin 10 is an unusual peptide of marine origin which binds to tubulin in the vinblastine/ maytansine/phomopsin-binding region and potently inhibits mitosis. Using N, N′-ethylenebis(iodoacetamide) (EBI) and iodo[14C]acetamide as probes for the effects of ligands on the thiol groups of tubulin, we found that dolastatin 10 has effects on the sulfhydryls indistinguishable from those of phomopsin A but quite different from those of vinblastine and maytansine. Using the binding of bis-5,5'-[8-(N-phenyl) aminonaphthalene-1-sulfonic acid](BisANS) as a measure of tubulin decay, we found that dolastatin 10 resembled phomopsin A in that decay was not detectable by this assay in its presence. Interestingly, both otherwise very different peptides are among the most effective inhibitors of tubulin decay yet discovered.
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