Subject: Fo Subunit of ATP Synthase and electro-motive force

Hello,

I was taught that Brownian motion drives the rotation of ATP Synthase. (I 
understand that the Proton gradient is necessary to allow ATP Synthase to 
turn.) 

Therefore, with no friction, the thermal energy in the environment, Ut ~ kT, 
should be equal to roughly 1/2 I w^2, where I is the moment of inertia and w 
is the angular velocity of the protein.

However, looking at the active site of the Fo subunit of ATP Synthase,

http://www.bio.cmu.edu/Courses/BiochemMols/Channels/1c17.htm,

I see that there is an Arg210 and Asp61 amino acid, within 2.73 A of each 
other. (Ignoring the other Asp amino acid which is 3.93 A away from the Arg. 

The Boltzmann constant is k~10^-23 J/K so that kT ~ 10^-21. The electrostatic 
potential energy caused between Arg210 and Asp61, ignoring other amino acids, 
would be 
Ue~q(arg210)q(Asp61)/(r eo). 1/eo ~10^9, and r~10^-10. Therefore Ue~10^19, 
while Ut~ 10^-21.

Therefore, it seems to me that ATP Synthase is not a pure Brownian motion 
motor, but may also be driven by an electro-static force, thus making ATP 
Synthase the world's smallest electric motor.

My question for you is whether ATP Synthase turns because of Brownian motion 
or because of an electrostatic force, or both and why.

Thanks,

- Peter Vandeventer

P.S.: Perhaps when Asp61 gets protonated, then there is a new electro-static 
attraction between the next, un-protonated Asp. This attraction may drive the 
rotation of the protein.

Re: Fo Subunit of ATP Synthase and electro-motive force