The stall torque of the bacterial flagellar motor.
The bacterial flagellar motor couples the flow of protons across the cytoplasmic membrane to the rotation of a helical flagellar filament. Using tethered cells, we have measured the stall torque required to block this rotation and compared it with the torque of the running motor over a wide range of values of proton-motive force and pH. The stall torque and the running torque vary identically: both appear to saturate at large values of the proton-motive force and both decrease at low or high pH. This suggests that up to speeds of approximately 5 Hz the operation of the motor is not limited by the mobility of its internal components or the rates of proton transfer reactions coupled to flagellar rotation.
D002462:Cell Membrane / Q000502:physiology; D005407:Flagella / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D009068:Movement; D013291:Streptococcus / Q000502:physiology*; D013314:Stress, Mechanical