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Updated: Aug 1, 2026

PIP-on-a-chip: A Label-free Study of Protein-phosphoinositide Interactions
Published on: July 27, 2017
The binding of physiologically significant protons to 2,3-diphosphoglycerate
This study determined the precise intrinsic pKa values for 2,3-diphosphoglycerate (DPG) protons using 31P-NMR spectroscopy, revealing key insights into its physiological behavior.
Area of Science:
- Biochemistry
- Chemical Physics
Background:
- 2,3-diphosphoglycerate (DPG) plays a crucial role in regulating hemoglobin's oxygen affinity.
- Accurate pKa values are essential for understanding DPG's function in vivo.
- Conventional titration methods may not fully capture the intrinsic protonation states of DPG.
Purpose of the Study:
- To determine the intrinsic pKa values of 2,3-diphosphoglycerate (DPG) protons in the physiologically relevant pH range (6.8-7.8).
- To compare these intrinsic values with apparent pKa values obtained from conventional acid-base titrations.
- To investigate the interaction energies between protonated phosphate groups on DPG.
Main Methods:
- Utilized 31P-NMR spectroscopy to monitor changes in phosphate chemical shifts as a function of pH.
- Applied statistical thermodynamic methods to analyze NMR data and calculate intrinsic pKa values.
- Generated a theoretical titration curve based on NMR-derived thermodynamic parameters.
Main Results:
- Intrinsic pKa values of 6.99 ± 0.07 (for C-3 phosphate) and 7.28 ± 0.04 (for C-2 phosphate) were determined.
- These differ significantly from apparent pKa values of 6.39 and 7.39 obtained via conventional titration.
- An interaction energy of +0.77 kcal/mol between the protonated phosphates was calculated.
Conclusions:
- 31P-NMR spectroscopy provides a more accurate determination of DPG's intrinsic pKa values compared to conventional methods.
- The determined intrinsic pKa values offer a refined understanding of DPG's protonation state and its physiological implications.
- The thermodynamic data can accurately predict DPG's titration behavior across a physiological pH range.
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