IMPLICATIONS OF DIFFUSION-CONTROLLED LIMIT FOR PROCESSIVITY OF DIMERIC KINESIN HEAD DOMAINS

The diffusion-limited rate for association of the ADP complex of dimer ic 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 h ighly elongated prolate ellipsoidal adsorber of 100% efficiency. This theoretical bimolecular rate is similar to 100-fold smaller than the e xperimental rate, k(cat)/K-0.5(MT), for DKH392 that was determined fro m 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 AT P molecules during each diffusional encounter with a microtubule.