Experimental thermodynamics of single molecular motor

Molecular motor is a nano-sized chemical engine that converts chemical free energy to mechanical motions. Hence, the energetics is as important as kinetics in order to understand its operation principle. We review experiments to evaluate the thermodynamic properties of a rotational F(1)-ATPase motor (F(1)-motor) at a single-molecule level. We show that the F(1)-motor achieves 100% thermo dynamic efficiency at the stalled state. Furthermore, the motor reduces the internal irreversible heat inside the motor to almost zero and achieves a highly-efficient free energy transduction close to 100% during rotations far from quasistatic process. We discuss the mechanism of how the F(1)-motor achieves such a high efficiency, which highlights the remarkable property of the nano-sized engine F(1)-motor.