Fig. 4.

Effects of nocodazol and Na₂CO₃ on membrane tubulin. Erythrocyte membranes (1 mg protein) were incubated in the presence (+) or absence (−) of 0.1 M Na₂CO₃, pH 11.5, for 15 min at 4 °C, or with 50 μM nocodazole for 30 min at room temperature, and centrifuged at 100,000×g for 30 min. The pellets were analyzed for total tubulin or, alternatively, were resuspended in TBS (300 μl) incubated with 300 μg/ml purified tubulin for 30 min at 37°C and centrifuged again at 100,000×g for 30 min. Aliquots of pellet fractions (250 μg protein) were analyzed for total tubulin using mAb DM1A. Optical density of tubulin bands was quantified using the Scion Image program. Values are shown in the lower panel as mean ± SD from three independent experiments, expressed as percentage relative to value from non-treated membranes