Table 2

Microtubule lengths after assembly with paclitaxel and discodermolide

DrugAverage polymer length (relative to lengths with paclitaxel)
MAPs and GTPMAPs onlyGTP onlyNo MAPs or GTP
μm
None4.3  ± 2  (2.3)
3.3  ± 2  (1.9)2-a
Paclitaxel1.9  ± 1  (1.0)2.6  ± 1  (1.0)6.0  ± 3  (1.0)
1.7  ± 0.6  (1.0)2-a
Discodermolide0.83  ± 0.4  (0.44)1.2  ± 0.6  (0.46)1.7  ± 1  (0.28)2.3  ± 1.3
0.58  ± 0.3  (0.34)2-a

Electron micrographs were taken of samples from reaction mixtures containing 1.0 mg/ml (10 μm) tubulin, 10 μmconcentration of drug, 4% (v/v) dimethyl sulfoxide, 0.1 mMES, pH 6.9, and, if present, 100 μm GTP and heat-treated MAPs at 0.5 mg/ml. Drug was the final addition to the reaction mixture. Reaction mixtures were incubated as described in Experimental Procedures. After 20 min at 37°, samples were applied to grids, which were used to prepare the micrographs used in the analyses presented in the table. Measurements were made on photographs at 4800× magnification for paclitaxel and without drug and 6000× for discodermolide. A minimum of 100 microtubules were measured for each reaction condition. Values are presented as mean ± standard deviation.

    • 2-a Data from Ref. 8, a separate experiment.