Determination of torque generation from the power stroke of Escherichia coli F1-ATPase

The torque generated by the power stroke of Escherichia coli F1-ATPase was determined as a function of the load from measurements of the velocity of the γ-subunit obtained using a 0.25 µs time resolution and direct measurements of the drag from 45 to 91 nm gold nanorods. This result was compared to values of torque calculated using four different drag models. Although the γ-subunit was able to rotate with a 20× increase in viscosity, the transition time decreased from 0.4 ms to 5.26 ms. The torque was measured to be 63 ± 8 pN nm, independent of the load on the enzyme.