  A master equation approach to molecular motors allows to describe a
mechano-chemical cyclic system where chemical and translational degrees of
freedom are treated on an equal footing. A generalized detailed balance
condition in the out of equilibrium regime is shown to be compatible with the
Fokker-Planck equation in the continuum limit. The Onsager reciprocity
relations hold for stationary states close to equilibrium, provided the
generalized detailed balance condition is satisfied. Semi-phenomenological
considerations in the case of motor proteins lead to a discrete kinetics model,
for which interesting observable quantities can be directly calculated and
compared with experimental data.
