  Two simple (rotator and one-particle) mechanistic models are suggested to
describe simultaneously at a minimal level of sophistication two basic
functions of F$_1$-ATPase: a motor regime driven by ATP hydrolysis and its
inverted function as ATP synthesis. This description is consistent with the
so-called rotary binding-change mechanism, a milestone of functioning ATP
synthase, and uses a stepping (driving) function associated with two sequences
of time instants, at which hydrolysis and synthesis reactions occur. It is
useful to analyse experimental data and numerical simulations indeed predict
corresponding dynamic behavior.
