F ₁-ATPase: A highly efficient rotary ATP machine

• A single molecule of F ₁-ATPase is by itself a rotary motor in which a central subunit, γ, rotates against a surrounding stator cylinder made of α ₃β ₃ hexamer. • Driven by the three β subunits that hydrolyse ATP sequentially, the motor runs with discrete 120° steps at low ATP concentrations. • Over broad ranges of load and speed, the motor produces a constant torque of 40 pN·nm. • The mechanical work the motor does in the 120° step, or the work per ATP hydrolysed, is also constant and amounts to 80-90 pN·nm, which is close to the free energy of ATP hydrolysis. Thus this motor can work at near 100% efficiency.