Single molecule thermodynamics of ATP synthesis by F1-ATPase

Abstract

F _o F _1 -ATP synthase is a factory for synthesizing ATP in virtually all cells. Its core machinery is the subcomplex F _1 -motor (F _1 -ATPase) and performs the reversible mechanochemical coupling. The isolated F _1 -motor hydrolyzes ATP, which is accompanied by unidirectional rotation of its central $\gamma -{\rm shaft}$ . When a strong opposing torque is imposed, the $\gamma $ -shaft rotates in the opposite direction and drives the F _1 -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 F _1 -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.

Keywords

• motor proteins
• nonequilibrium and irreversible thermodynamics
• F1-ATPase