Implications of diffusion-controlled limit for processivity of dimeric kinesin head domains

The diffusion-limited rate for association of the ADP complex of dimeric DKH392 kinesin head domains with a microtubule was estimated to be 2-3 x 10(7) M-1 s-1 based on approximation of a microtubule as a highly elongated prolate ellipsoidal adsorber of 100% efficiency. This theoretical bimolecular rate is approximately 100-fold smaller than the experimental rate, kcat/KMT0.5, for DKH392 that was determined from the stimulation of the steady-state ATPase rate by microtubules. The large difference between these two estimates of the bimolecular rate indicates that it is likely that dimeric DKH392 hydrolyzes multiple ATP molecules during each diffusional encounter with a microtubule.