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The Final Frontier of pH and the Undiscovered Country Beyond

Bal, Wojciech and Kurowska, Ewa and Maret, Wolfgang (2012) The Final Frontier of pH and the Undiscovered Country Beyond. PloS one . ISSN 1932-6203



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, Kw = [H+]6[OH2].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 volume VpH required to provide a physical meaning to Kw, VpH~10DpH{pKw=2D| 10pKw=2 NA (where NA is Avogadro’s number). 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vesicles and lysosomes, are too small to contain free H+ ions at equilibrium, thus the definition of pH based on Kw is no longer valid.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. These results indicate that pH fails to describe intracellular conditions, and that water appears to be dissociated too weakly to provide free H+ ions as a general source for biochemical reactions. Consequences of this finding are discussed.

Item Type:Article
Subjects:Q Science > QD Chemistry
Divisions:Department of Biophysics
ID Code:480
Deposited By: Prof Wojciech Bal
Deposited On:03 Apr 2013 08:57
Last Modified:13 Oct 2014 13:35

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