The effect of taxol on microtubule proteins at 0°C is controversial. In order to determine if taxol is unable to bind to unassembled tubulin, as has been hypothesized, the binding of [3H]acetyl taxol has been studied using equilibrium microdialysis. Ac-taxol bound to microtubules at 37°C and the binding remained stable when the temperature was lowered to 0°C. Ac-taxol bound also at 0°C to microtubules stabilized with rhazinilam. In contrast, there was no binding of Ac-taxol to unassembled tubulin, either free tubulin at 0°C or tubulin, complexed with several microtubule poisons, at 0 and 37°C.
