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The Effect of Salt on Protein Chemical Potential Determined by Ternary Diffusion in Aqueous Solutions

Summary: The Effect of Salt on Protein Chemical Potential Determined by Ternary Diffusion in
Aqueous Solutions
Onofrio Annunziata,*, Luigi Paduano,, Arne J. Pearlstein, Donald G. Miller,,| and
John G. Albright
Department of Chemistry, Texas Christian UniVersity, Fort Worth, Texas 76129, Geosciences and
EnVironmental Technologies, Lawrence LiVermore National Laboratory, P.O. Box 808,
LiVermore, California 94551, Department of Mechanical and Industrial Engineering,
UniVersity of Illinois at Urbana-Champaign, 1206 West Green Street, Urbana, Illinois 61801, and
Dipartimento di Chimica, UniVersita` di Napoli "Federico II", Naples, 80126, Italy
ReceiVed: August 12, 2005; In Final Form: October 8, 2005
We use accurate thermodynamic derivatives extracted from high-precision measurements of the four volume-
fixed diffusion coefficients in ternary solutions of lysozyme chloride in aqueous NaCl, NH4Cl, and KCl at
pH 4.5 and 25 C to (a) assess the relative contributions of the common-ion and nonideality effects to the
protein chemical potential as a function of salt concentration, (b) compare the behavior of the protein chemical
potential for the three salts, which we found to be consistent with the Hofmeister series, and (c) discuss our
thermodynamic data in relation to the dependence of the protein solubility on salt concentration. The four
diffusion coefficients are reported at 0.6 mM lysozyme chloride and 0.25, 0.5, 0.9, 1.2, and 1.5 M KCl and
extend into the protein-supersaturated region. The chemical potential cross-derivatives are extracted from
diffusion data using the Onsager reciprocal relation and the equality of molal cross-derivatives of solute
chemical potentials. They are compared to those calculated previously from diffusion data for lysozyme in


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


Collections: Chemistry