Fluctuation driven ratchets: Molecular motors

The motion of a heavily damped Brownian particle in a periodic potential subject to a dichotomously fluctuating perturbation is considered. We show that even if the net force is always zero, flow is induced by a fluctuation of the energy barrier, but only at flipping times roughly in between the adiabatic adjustment times on the left and right of the barrier. Predictions of our model are consistent with recent experimental data obtained by Svoboda et al. Nature (London) 365, 721--727 (1993) for a single kinesin molecule moving along a biopolymer.