Conclusions

The presence of numerous, closely-spaced binding sites decreases the mobility of taxol inside microtubules. Taxol binds with too great an affinity to experience facilitated diffusion on the microtubule substrate. Ligands with weak binding may move quicker throughout a cell by binding and rebinding to microtubules. Experiment should be repeated on single microtubules to eliminate the effects of the bundles. Similar methods could be used on fluorescent derivatives of other microtubule ligands, such as kinesin and tau, to determine relative on and off rates.