the final frontier of ph and the undiscovered country beyond最后边界的ph值和未被发现的国家之外.pdf

The Final Frontier of pH and the Undiscovered Country Beyond 1 1 2 Wojciech Bal *, Ewa Kurowska , Wolfgang Maret 1 Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland, 2 King’s College London, Diabetes and Nutritional Sciences Division, London, United Kingdom Abstract The comparison of volumes of cells and subcellular structures with the pH values reported for them leads to a conflict with the definition of the pH scale. The pH scale is based on the ionic product of water, K + 2 w = [H ] 6[OH ].We used Kw [in a reversed way] to calculate the number of undissociated H2O molecules required by this equilibrium constant to yield at least one of its daughter ions, H+ or OH2 at a given pH. In this way we obtained a formula that relates pH to the minimal pKw =2 10 volume VpH required to provide a physical meaning to Kw, VpH ~10DpH {pKw =2D | (where NA is Avogadro’s number). NA For example, at pH 7 (neutral at 25uC) VpH = 16.6 aL. Any deviation from neutral pH results in a larger VpH value. Our results indicate that many subcellular structures, including coated vesicles and lysosomes, are too small to contain free H+ ions at equilibrium, thus the definition of pH based on Kw is no longer valid. Larger subcellular structures, such as mitochondria, apparently contain only a few free H+ ions. Thes