Role of directional fidelity in multiple aspects of extreme performance of the F(1)-ATPase motor.

Quantitative understanding of the best possible performance of nanomotors allowed by physical laws pertains to the study of nanomotors from biology as well as nanotechnology. The biological nanomotor F(1) ATPase is the best available model system as it is the only nanomotor known for extreme energy conversion near the limit of energy conservation. Using a unified theoretical framework centered on a concept called directional fidelity, we analyze recent experiments in which the F(1) motor's performance was measured for controlled chemical potentials and expose from the experiments quantitative evidence for the motor's multiple extreme performances in directional fidelity, speed, and catalytic capability close to physical limits. Specifically, the motor nearly exhausts the available energy from the fuel to retain the highest possible directional fidelity for an arbitrary load, encompassing the motor's extreme energy conversion and beyond. The theory-experiment comparison implies a tight chemomechanical coupling up to stalemate as futile steps occur, but unlikely involve fuel consumption. The F(1)-motor data also help clarify the relation between directional fidelity and experimentally measured stepping ratio.