Tubulin thiols were measured in 100,000 × g supernates isolated from A- IMR-32 cells, B-cortical neurons and C- E19 brain. To measure tubulin thiols, supernates were first treated with N-ethyl maleimide to block free thiols, followed by reduction with dithiothreitol, and reaction with IAF as described in Material and Methods. After SDS-PAGE, the fluorescence intensity of the tubulin bands was quantitated. Results are shown as means ± SEM of 4 independent experiments for IMR-32 cells and cortical neurons, or 5-7 litters for GD19 brain. *Significantly different compared with the other groups (p<0.05, one-way ANOVA test).