PATHWAY OF PROCESSIVE ATP HYDROLYSIS BY KINESIN

Direct measurement of the kinetics of kinesin dissociation from microt ubules, the release of phosphate and ADP from kinesin, and rebinding o f kinesin to the microtubule have defined the mechanism for the kinesi n ATPase cycle. The processivity of ATP hydrolysis is ten molecules pe r site at low salt concentration but is reduced to one ATP per site at higher salt concentration. Kinesin dissociates from the microtubule a fter ATP hydrolysis. This step is rate-limiting. The subsequent rebind ing of kinesin ADP to the microtubule is fast, so kinesin spends only a small fraction of its duty cycle in the dissociated state. These res ults provide an explanation for the motility differences between skele tal myosin and kinesin.