Simple mechanism whereby the F₁-ATPase motor rotates with near-perfect chemomechanical energy conversion

F₁-ATPase is a motor enzyme in which a central shaftγsubunit rotates 120° per ATP in the cylinder made of α₃β₃ subunits. During rotation, the chemical energy of ATP hydrolysis (ΔG ATP) is converted almost entirely into mechanical work by an elusive mechanism. We measured the force for rotation (torque) under various ΔG ATPconditions as a function of rotation angles of theγsubunit with quasi-static, single-molecule manipulation and estimated mechanical work (torque × traveled angle) from the area of the function. The torque functions show three sawtooth-like repeats of a steep jump and linear descent in one catalytic turnover, indicating a simple physical model in which the motor is driven by three springs aligned along a 120° rotation angle. Although the second spring is unaffected by ΔG ATP, activation of the first spring (timing of the torque jump) delays at low [ATP] (or high [ADP]) and activation of the third spring delays at high [Pi]. These shifts decrease the size and area of the sawtooth (magnitude of the work). Thus, F₁-ATPase responds to the change of ΔG ATPby shifting the torque jump timing and uses ΔG ATPfor the mechanical work with near-perfect efficiency.