  The simplest mechanism for molecular electron pumps is discussed which is
based on nonadiabatic electron tunnelling and nonequilibrium conformational
fluctuations. Such fluctuations can be induced, e.g. by random binding of
negatively charged ATP molecules to the electron-transferring molecular
complex, their subsequent hydrolysis and the products dissociation. The pumping
rate can be controlled by the ATP concentration in solution. Depending on the
model parameters there may exist a critical ATP concentration for the pump to
function. Alternatively, nonequilibrium fluctuations can be induced by
externally applied stochastic electric fields. For realistically chosen
parameters, the mechanism is shown to be robust and highly efficient.
