  Bartussek, Hanggi and Kissner studied a rocking ratchet system, in which a
Brownian particle is subject to an asymmetric periodic potential together with
an oscillating force, and found that the direction of the macroscopic current
can be reversed by changing the parameter values characterizing the model
[Europhys. Lett., 28 (1994) 459]. In this letter, we apply their ratchet theory
to a rotary motor-protein, F1-ATPase. In this work, we construct a model of a
rocking ratchet in which F1-ATPase rotates not as a result of ATP hydrolysis
but through the influence of an oscillating force. We then study the motion of
F1-ATPase on the basis of molecular dynamics simulations of this coarse-grained
protein model. Although in the absence of ATP, F1-ATPase exhibits directionless
Brownian motion when there exists no oscillating force, we observe directional
motion when we do apply an oscillating force. Furthermore, we observe that the
direction of rotation is reversed when we change the oscillation frequency.
