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The binding of physiologically significant protons to 2,3-diphosphoglycerate

Authors
Journal
Biophysical Chemistry
0301-4622
Publisher
Elsevier
Publication Date
Volume
18
Issue
4
Identifiers
DOI: 10.1016/0301-4622(83)80054-4
Keywords
  • Pka
  • Diphosphoglycerate
  • Proton Binding
  • Free Energy
Disciplines
  • Biology
  • Chemistry
  • Physics

Abstract

Abstract The intrinsic p K a values of protons of 2,3-diphosphoglycerate (DPG) which titrate in the physiologically significant range (i.e., pH 6.8–7.8) have been determined by measuring the changes in chemical shifts of the two phosphate resonances of the molecule as a function of pH using 31P-NMR spectroscopy. While conventional acid-base titration techniques resulted in apparent p K a values of 6.39 and 7.39 for these protons, analysis of the 31P-NMR data by statistical thermodynamic methods yielded intrinsic p K a, values of 6.99±0.07 and 7.28 ±0.04, for protons associated with the phosphates bound to carbon-3 (C-3) and carbon-2 (C-2), respectively, with an interaction energy of + 0.77 kcal/mol. The free energies for the binding of protons to the C-2 and C-3 phosphates and the associated interaction energies determined by 31P-NMR were used to generate a theoretical titration curve which was essentially identical to that determined by conventional acid-base titration. The physiological implications of this work are briefly discussed.

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