The Lee proton-electrostatics hypothesis is a revolutionary scientific theory that is challenging certain assumptions made in the field of bioenergetics in regards to ATP synthesis in biological systems, specifically alkalophilic bacteria. This study provides experimental support for the Lee proton-electrostatics hypothesis by further demonstrating evidence of a localized proton layer existing at the water-membrane interface in a simulated biological membrane apparatus. Divalent cations pose a unique problem in terms of studying cation equilibrium exchange. Contrary to their alkali metal counterparts, divalent bicarbonate salts are less soluble, and cannot exist outside of solution. Whilst monovalent cations have been studied extensively, divalent cation exchange has not been studied experimentally. A previous study determined sodium cation equilibrium exchange and potassium cation exchange to be (5.07 ± 0.46) x 10-8 and (6.93 ± 0.91) x 10-8 respectively. There are factors facilitating greater exchange rate in magnesium compared to its monovalent cation counterparts. We surmise that an equilibrium exchange occurs at 0.85 mM Mg(HCO3)2. The findings contained therein contributed to the successful determination of the equilibrium constant between Mg2+ ions and the localized proton layer for the Mg2+ non-proton cation. The equilibrium constant for Mg2+ cations to exchange with the electrostatically localized protons was determined to be (1.56 ± 0.46) x 10-5. The equilibrium constant, much smaller than one, thus provides support for Lee’s proton electrostatic localization model since so many more magnesium cations in the bulk liquid phase that are required to even partially delocalize just a single proton at the membrane-water interface. These results are relevant to further understand how water can act as a proton conductor for proton coupling energy transduction and the implications of different biological organisms’ salinity tolerance.

Investigation of magnesium cation-proton exchange at an electrostatic localized membrane interface: Fundamental to bioenergetics

ACS Spring 2022

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