Figure 5.

MT bundles display a higher sensitivity than MTs to brief cold shock. (A) Temperature variations inside the spectrophotometer cuvette versus time after 2 min cold exposure. (B) Taxol-stabilized MTs are not released from bundles upon 2-min cold exposure. When cold exposure was applied to taxol-stabilized bundles formed in the presence of Spm, only a small absorbance variation was observed during cold shock. (C) Absorbance variations of MTs versus Spm concentration. A quantity of 30 μM tubulin was allowed to polymerize in the absence or presence of Spm. When the absorbance reached its plateau value, a brief cold shock was applied to the sample (see (A)). (D) When 1 mM Spm was added to a solution containing preformed MTs (30 μM tubulin), bundling was hindered and the sensitivity to the short cold shock significantly decreased. AFM imaging showed that isolated MTs or thin bundles (1) were present under such conditions, whereas thick and short bundles were formed when Spm was present from the beginning of tubulin polymerization (2).