  We study the ensemble velocity of non-processive motor proteins, described
with multiple chemical states. In particular, we discuss the velocity as a
function of ATP concentration. Even a simple model which neglects the
strain-dependence of transition rates, reverse transition rates and
nonlinearities in the elasticity can show interesting functional dependencies,
which deviate significantly from the frequently assumed Michaelis-Menten form.
We discuss how the oder of events in the duty cycle can be inferred from the
measured dependence. The model also predicts the possibility of velocity
reversal at a certain ATP concentration if the duty cycle contains several
conformational changes of opposite directionalities.
