A novel method for detecting F
1-ATPase rotation in a manner sufficiently sensitive to achieveacquisition rates
with a time resolution of 2.5
![](/images/entities/mgr.gif)
s (equivalent to 400 000 fps) is reported. This is sufficientfor resolving the rate at
which the
![](/images/gifchars/gamma.gif)
-subunit travels from one d
well state to another (transition time).Rotation is detected via a gold nanorod attached to the rotating
![](/images/gifchars/gamma.gif)
-subunit of an immobilized F
1-ATPase.Variations in scattered light intensity allo
w precise measurement of changes in the angular position of therod belo
w the diffraction limit of light. Using this approach, the transition time of
Escherichia coli F
1-ATPase
![](/images/gifchars/gamma.gif)
-subunit rotation
was determined to be 7.62 ± 0.15 (standard deviation) rad/ms. The averagerate-limiting d
well time bet
ween rotation events observed at the saturating substrate concentration
was8.03 ms, comparable to the observed Mg
2+-ATPase
kcat of 130 s
-1 (7.7 ms). Histograms of scattered lightintensity from ATP-dependent nanorod rotation as a function of polarization angle allo
wed the determinationof the nanorod orientation
with respect to the axis of rotation and plane of polarization. This informationallo
wed the drag coefficient to be determined,
which implied that the instantaneous torque generated byF
1 was 63.3 ± 2.9 pN nm. The high temporal resolution of rotation allo
wed the measurement of theinstantaneous torque of F
1, resulting in direct implications for its rotational mechanism.