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

F-1-ATPase is a motor enzyme in which a central shaft. subunit rotates 120 degrees per ATP in the cylinder made of alpha(3)beta(3) subunits. During rotation, the chemical energy of ATP hydrolysis (Delta G(ATP)) is converted almost entirely into mechanical work by an elusive mechanism. We measured the force for rotation (torque) under various Delta G(ATP) conditions as a function of rotation angles of the gamma subunit with quasistatic, single-molecule manipulation and estimatedmechanical work (torque x 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 degrees rotation angle. Although the second spring is unaffected by Delta G(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 [P-i]. These shifts decrease the size and area of the sawtooth (magnitude of the work). Thus, F-1-ATPase responds to the change of Delta G(ATP) by shifting the torque jump timing and uses Delta G(ATP) for the mechanical work with near-perfect efficiency.