Prof. Signe Kjelstrup (Norwegian University of Science and Technology)
We show that the kinetics of a molecular motor fuelled by ATP and operating betweeen a deactivated and activated state, can be derived from the principles of non-equilibrium thermodynamics for the mesoscopic domain [1, 2]. As example we study muscle contraction. The activation by ATP, the possible slip of the motor, as well as the forward stepping carrying a load, are viewed as slow diffusion along a reaction coordinate. Local equilibrium is assumed in the reaction coordinate spaces, making it possible to derive the non-equilibrium thermodynamic description. Using this scheme, we find non-linear expressions for the velocity of the motor, in terms of the driving force along the spacial coordinate, and in terms of the chemical potentials of the reactants and products which maintain the cycle. The second law efficiency is defined, and the velocity corresponding to maximum power is obtained. Experimental results taken from the literature , support the description, and give a maximum efficiency near 0.6 at a muscle filament velocity of 5Å/ms. The formalism proposed can be applied to other non-equilibrium activated processes, say of protein binding or DNA stretching. It opens the possibility for detailed molecular models, which may be needed to explain experiments. References  S. Kjelstrup, J.M. Rubi, D. Bedeaux, Phys. Chem. Chem. Phys. 2005, 7, 4009.  A. Lervik, D. Bedeaux, and S. Kjelstrup, Eur. Biophys. J. 2012, 41, 437  T. Førland, Biophys. J. 1985, 47, 665.