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The Effect of Salt Stoichiometry on Protein-Salt Interactions Determined by Ternary Diffusion in Aqueous Solutions
 

Summary: The Effect of Salt Stoichiometry on Protein-Salt Interactions Determined by Ternary
Diffusion in Aqueous Solutions
Onofrio Annunziata,*, Luigi Paduano,, and John G. Albright
Department of Chemistry, Texas Christian UniVersity, Fort Worth, Texas 76129, and Dipartimento di Chimica,
UniVersita` di Napoli "Federico II", Naples, 80126, Italy
ReceiVed: March 15, 2006; In Final Form: June 15, 2006
We report the four diffusion coefficients for the lysozyme-MgCl2-water ternary system at 25 C and pH
4.5. The comparison with previous results for the lysozyme-NaCl-water ternary system is used to examine
the effect of salt stoichiometry on the transport properties of lysozyme-salt aqueous mixtures. We find that
the two cross-diffusion coefficients are very sensitive to salt stoichiometry. One of the cross-diffusion
coefficients is examined in terms of common-ion, excluded-volume, and protein-preferential hydration effects.
We use the four ternary diffusion coefficients to extract chemical-potential cross-derivatives and protein-
preferential interaction coefficients. These thermodynamic data characterize the protein-salt thermodynamic
interactions. We demonstrate the presence of the common-ion effect (Donnan effect) by analyzing the
dependence of the preferential-interaction coefficient not only with respect to salt concentration but also with
respect to salt stoichiometry. We conclude that the common-ion effect and the protein-preferential hydration
are both important for describing the lysozyme-MgCl2 thermodynamic interaction.
Introduction
The chemical potential of a protein component in aqueous
solution is significantly affected by the presence of hydration,

  

Source: Annunziata, Onofrio - Department of Chemistry, Texas Christian University

 

Collections: Chemistry