Inhibition of microtubule assembly by actinomycin D, an anti-tumour drug

Effect of actinomycin D, an antibiotic, was investigated on the biological function of tubulin from bovine brain. The microtubule assembly was inhibited nearly completely when an equal molar ratio of actinomycin D and tubulin was used. The depolymerisation of the same, however, was not altered under the same conditions. The competence of tubulin to bind colchicine and GTP was also not affected. Chromatographic and the spectrophotometric studies showed that 0.94 mol of actinomycin D binds per mole of tubulin.