Differences in microtubule stability to colchicine in extracts of guinea pig, rat and rabbit brain.

1. Microtubules (MT) from a guinea pig brain 25,000 g supernatant are not depolymerized by colchicine in contrast to MT from similar preparations of rat and rabbit. 2. The colchicine-stability was lost if the guinea pig brain homogenate was centrifuged at a higher g-level, further purified or if only the grey matter was used. 3. The association constant of colchicine to tubulin did not differ between a stable and a labile guinea pig brain preparation. 4. The GTP-hydrolysis was higher in the guinea pig preparation containing stable MT, than in the preparation containing labile MT. Additional GTP added to the polymerized MT before colchicine exposure, labilized the MT. Preincubation with NaF decreased the GTP-hydrolysis and caused a colchicine depolymerization. 5. The results indicate species differences in colchicine sensitivity of in vitro polymerized MT, probably depending on differences in GTP-hydrolysis.