Before revision:  Here, we evaluated the work exerted by the nanosized biological free-energy transducer F1-ATPase by single-molecule experiments on the basis of nonequilibrium theory . The results imply that the F1-ATPase achieves a nearly 100\% free-energy conversion efficiency even far from quasistatic process for both the mechanical-to-chemical and chemical-to-mechanical transductions. Such a high efficiency at a finite-time operation is not expected for macroscopic engines and highlights a remarkable property of the nanosized engines working in the energy scale of kBT .
After revision:  Here, we determined the amount of mechanical work exploited by the F_1-motor to synthesize an ATP molecule during forced rotations using methodology combining a nonequilibrium theory and single molecule measurements of responses to external torque. We found that the work exploited by the motor amounts only to that is thermodynamically required for the ATP synthesis. Specifically, F_1-motor converts mechanical work to chemical free energy at quite a high efficiency at a finite-time operation is not expected for macroscopic engines and highlights a remarkable property of the nanosized engines working in the energy scale of kBT .