Function of the F1-motor (F1-ATPase) of ATP synthase by apolar-polar repulsion through internal interfacial water

At the β-P end of ADP · Mg occurs an inorganic phosphate, Pi. This Pi resides at the base of a water-filled cleft that functions like an aperture to focus, into an aqueous chamber, a competition for hydration (an apolar-polar repulsion) between charged phosphate and hydrophobic surface of the γ-rotor. Two means available for the phosphate and the hydrophobic surface to improve their hydration free energies are physically to separate by rotation of the γ-rotor or chemically to combine Pi with ADP to form less charged ATP. This proposal derives from calculated changes in Gibbs free energy for hydrophobic association of amino acid side chains and chemical modifications thereof and from experimentally demonstrated water-mediated repulsion between hydrophobic and charged sites that resulted from extensive studies on designed elastic-contractile model proteins.