Table 1

Critical concentrations of tubulin for assembly with paclitaxel and discodermolide

DrugCritical concentration of tubulin
MAPs and GTP1-aMAPs onlyGTP onlyNo MAPs or GTP
Paclitaxel0.24  ± 0.31.7  ± 0.44.3  ± 0.422  ± 1
Discodermolide0.41  ± 0.40.93  ± 0.20.88  ± 0.43.0  ± 0.3

Critical concentrations were measured in reaction mixtures containing 10 μm drug, 4% (v/v) dimethyl sulfoxide, 0.1m MES (pH 6.9), and, if present, 100 μm GTP and MAPs at half the concentration (in mg/ml) of tubulin. Drug was the final addition to the reaction mixture. Critical concentrations were determined from final turbidity readings at 350 nm, with turbidity plotted against the tubulin concentration. The critical concentration was taken as the intercept on the concentration axis. Data are presented as concentration ± standard error of at least two independent experiments. For additional details, see Ref. 13. The data were analyzed by linear regression using the software program Origin (Microcal Software, Northampton, MA).

    • 1-a Without drug, the tubulin critical concentration under this reaction condition was 3.0 ± 0.05 μm.