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FO-ATP synthase (FO) is a rotary motor that converts potential energy from ions, usually protons, moving from high- to low-potential sides of a membrane into torque and rotary motion. Here we propose a mechanism whereby electric fields emanating from the proton entry and exit channels act on asymmetric charge distributions in the c-ring, due to protonated and deprotonated sites, and drive it to rotate. The model predicts a scaling between time-averaged torque and proton motive force, which can be hindered by mutations that adversely affect the channels. The torque created by the c-ring of FO drives the γ-subunit to rotate within the ATP-producing complex (F1) overcoming, with the aid of thermal fluctuations, an opposing torque that rises and falls with angular position. Using the analogy with thermal Brownian motion of a particle in a tilted washboard potential, we compute ATP production rates vs. proton motive force. The latter shows a minimum, needed to drive ATP production, which scales inversely with the number of proton binding sites on the c-ring. [ABSTRACT FROM AUTHOR]

We report the nonlinear response of tissue and nerve fibers in the earthworm Lumbricus terrestris to sinusoidal electric field excitations. A High-Tc Superconducting Quantum Interference Device (SQUID) magnetometer detects the magnetic field generated by complex currents in the animal. SQUID signals are processed on a Fast Fourier Transform (FFT) spectrum analyser. Use of the SQUID eliminates low frequency polarization impedance and field distortion that would be present near pickup electrodes. Electrical 4-probe harmonic response measurements of the excised nerve fiber are then compared to the driven Hodgkin-Huxley active transport model. [ABSTRACT FROM AUTHOR]