A mechano-chemiosmotic model for the coupling of electron and proton transfer to ATP synthesis in energy-transforming membranes: a personal perspective

ATP is synthesized using ATP synthase by utilizing energy either fromthe oxidation of organic compounds, or from light, via redox reactions (oxidative-or photo phosphorylation), in energy-transforming membranes of mitochondria, chloroplasts, and bacteria. ATP synthase undergoes several changes during its functioning. The generally accepted model for ATP synthesis is the well-known rotatory model (see e.g., Junge et al., Nature 459: 364-370, 2009; Junge and Muller, Science 333: 704-705, 2011). Here, we present an alternative modified model for the coupling of electron and proton transfer to ATP synthesis, which was initially developed by Albert Lester Lehninger (1917-1986). Details of the molecular mechanism of ATP synthesis are described here that involves cyclic low-amplitude shrinkage and swelling of mitochondria. A comparison of the well-known current model and the mechano-chemiosmotic model is also presented. Based on structural, and other data, we suggest that ATP synthase is a Ca2+/H+-K+Cl--pump-pore-enzyme complex, in which gamma-subunit rotates 360 degrees in steps of 30 degrees, and 90 degrees due to the binding of phosphate ions to positively charged amino acid residues in the N-terminal gamma-subunit, while in the electric field. The coiled coil b(2)-subunits are suggested to act as ropes that are shortened by binding of phosphate ions to positively charged lysines or arginines; this process is suggested to pull the alpha(3)beta(3)-hexamer to the membrane during the energization process. ATP is then synthesized during the reverse rotation of the gamma-subunit by destabilizing the phosphated N-terminal gamma-subunit and b(2)-subunits under the influence of Ca2+ ions, which are pumped over from storage-intermembrane space into the matrix, during swelling of intermembrane space. In the process of ATP synthesis, energy is first, predominantly, used in the delivery of phosphate ions and protons to the a3b3-hexamer against the energy barrier with the help of C-terminal alpha-helix of gamma-subunit that acts as a lift; then, in the formation of phosphoryl group; and lastly, in the release of ATP molecules from the active center of the enzyme and the loading of ADP. We are aware that our model is not an acceptedmodel for ATP synthesis, but it is presented here for further examination and test.