H/D isotope effects on protein hydration and interaction in solution

Gen Physiol Biophys. 2006 Sep;25(3):303-11.

Abstract

An approach has been suggested to study the H/D isotope effect on protein-water and protein-protein intermolecular interactions by determining the content of non-freezing water using low-temperature (1)H NMR in mixed (H2O/D2O) water solutions. Direct data are obtained on the amount of H2O adsorbed (absolute hydration) in presence of the heavy isotope (deuterium D), and isothermals of H2O/D2O fractionation at protein surface groups are presented for temperatures between -10 degrees C and -35 degrees C and solutions of varying composition. The fractionation factor, phi = [x/(1 - x)]/[x(0)/(1 - x(0))], where x and x(0) are the fractions of deuterons in hydration and bulk water, respectively, appeared to be extremely high: phi >> 1 at 0.03 < x(0) < 0.10. The high values of phi indicate a decrease in apparent hydration of protein molecules. A probable reason of the effect can be an inter-protein molecular solvent-mediated interaction induced by D2O. The excess of phi over 1 appears to provide a quantitative estimate of the fraction of hydration water affected by such interaction.

MeSH terms

  • Animals
  • Deuterium / chemistry
  • Deuterium Oxide
  • Hemoglobin A / chemistry
  • Horses
  • Humans
  • Hydrogen / chemistry
  • Immunoglobulin G / chemistry
  • In Vitro Techniques
  • Methemoglobin / chemistry
  • Nuclear Magnetic Resonance, Biomolecular
  • Proteins / chemistry*
  • Solutions
  • Water

Substances

  • Immunoglobulin G
  • Proteins
  • Solutions
  • Water
  • Hydrogen
  • Methemoglobin
  • Hemoglobin A
  • Deuterium
  • Deuterium Oxide