FIG. 4.

Kinetics of K · ADP binding to the microtubule. a, Stopped-flow record for an experiment in which 2 μM K401 · ADP was rapidly mixed with 5 μM tubulin. Smooth line shows the fit to an exponential followed by a linear phase with the observed exponential rate at 90 s⁻¹. b, Microtubule concentration dependence of the rate of binding by K401. Data were fitted to a straight line; the slope gives the apparent second-order rate constant for microtubule binding (19.5 ± 0.7 μM⁻¹ s⁻¹).