title: The effect of salt stoichiometry on protein-salt interactions determined by ternary diffusion in aqueous solutions.
abstract: We report the four diffusion coefficients for the lysozyme-MgCl2-water ternary system at 25 degrees 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.
authors.affiliation: Department of Chemistry, Texas Christian University, Fort Worth, Texas 76129, USA. O.Annunziata@tcu.edu
authors.forename: Onofrio
authors.initials: O
authors.lastname: Annunziata
authors.forename: Luigi
authors.initials: L
authors.lastname: Paduano
authors.forename: John G
authors.initials: JG
authors.lastname: Albright
mesh_terms: D004058:Diffusion; D015636:Magnesium Chloride / Q000737:chemistry*; D009113:Muramidase / Q000737:chemistry*; D012965:Sodium Chloride / Q000737:chemistry; D012996:Solutions / Q000737:chemistry; D013237:Stereoisomerism; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D012996:Solutions; D015636:Magnesium Chloride; D014867:Water; D012965:Sodium Chloride; D009113:Muramidase