[In vitro study of tubulin polymerisation. Effects of ATP, vinblastine and isaxonine (author's transl)].

The dual action of vinblastine on tubulin, namely disruption and aggregation, is analyzed by turbidimetry. The existence of two different binding sites for the alkaloid is confirmed. The high affinity site binds vinblastine at low concentrations, at which no effect is observed on depolymerized tubulin, but where pre-formed microtubules are disrupted. The low affinity site is associated with tubulin aggregation. The binding constants of these two sites have been evaluated. Isaxonine (N-isopropyl-amino-2 pyrimidine) partially inhibits the effects of vinblastine, both on microtubule disruption and tubulin aggregation.