Single molecule thermodynamics of ATP synthesis by F₁-ATPase

F_oF₁-ATP synthase is a factory for synthesizing ATP in virtually all cells. Its core machinery is the subcomplex F₁-motor (F₁-ATPase) and performs the reversible mechanochemical coupling. The isolated F₁-motor hydrolyzes ATP, which is accompanied by unidirectional rotation of its central γ-shaft. When a strong opposing torque is imposed, the γ-shaft rotates in the opposite direction and drives the F₁-motor to synthesize ATP. This mechanical-to-chemical free-energy transduction is the final and central step of the multistep cellular ATP-synthetic pathway. Here, we determined the amount of mechanical work exploited by the F₁-motor to synthesize an ATP molecule during forced rotations using a methodology combining a nonequilibrium theory and single molecule measurements of responses to external torque. We found that the internal dissipation of the motor is negligible even during rotations far from a quasistatic process.