On the kinetics that moves Myosin V

•We emphasize the kinetic aspect or stochastic transport in terms of dynamical activity.•The motion of molecular motors such as Myosin V is due to an asymmetry in dynamical activity.•We predict a fluctuation symmetry.

Molecular motor proteins such as Myosin V, Dynein or Kinesin are no ratchets, at least not with a flashing asymmetric potential; the crucial asymmetry is in the dynamical activity. We make that explicit in terms of a simple Markov model, emphasizing the kinetic (and non-thermodynamic) aspects of stochastic transport. The analysis shows the presence of a fluctuation symmetry in that part of the dynamical activity which is antisymmetric under reversal of trailing and leading head of the motor. The direction of the motor motion is determined by it.