Kinetic modeling of rotary CF0F1-ATP synthase: storage of elastic energy during energy transduction.

F0F1-ATP synthase uses proton-motive force to produce ATP from ADP and Pi. With regard to its rotary mechanics, this energy transducing molecular machine assumes a unique position among all enzymes. In the work presented here we put forward a detailed functional model which is based on experimental results obtained with ATP synthase from spinach chloroplasts. We focus on the role of the elastic element, realized by the stalk-like subunit gamma, whose function is energy transduction between F0 and F1 taking into account the H+/ATP coupling ratio of four. Fitting parameters are the rate constants and the torsional rigidity of gamma, which have been adjusted according to the experimental results where the influence of transmembrane DeltapH on the rates of ATP synthesis/hydrolysis is put to the test. We show that the input and output of torsional energy are regulated by purely statistical principles, giving rise to the amount of transiently stored energy to be sliding, depending on DeltapH. During conditions of maximal turnover gamma turns out to be wound up towards 102 degrees which corresponds to a torque of 5.3. 10-20 N.m.