Microtubule-macrotubule transitions: intermediates after exposure to the mitotic inhibitor vinblastine.

Vinblastine treatment of microtubule protein or intact microtubules assembled in vitro produced bifilar rings and bifilar helices. Suspentsions of rings and helices were demonstrated to bind [(3)H]colchicine, a diagnostic property of microtubule protein. Macrotubules are suggested to consist of tightly coiled helices formed by longitudinal compacting of loosely coiled protofilament pair intermediates.