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Multicomponent Diffusion of Lysozyme in Aqueous Calcium Chloride. The Role of Common-Ion Effects and Protein-Salt Preferential Interactions
 

Summary: Multicomponent Diffusion of Lysozyme in Aqueous Calcium Chloride. The Role of
Common-Ion Effects and Protein-Salt Preferential Interactions
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 27, 2007; In Final Form: June 14, 2007
To investigate the effect of calcium salts on the thermodynamic and transport properties of aqueous solutions
of proteins, we report ternary diffusion coefficients for the lysozyme-CaCl2-water ternary system at 25 C
and pH 4.5. We have used our ternary diffusion coefficients to calculate preferential-interaction coefficients
as a function of salt concentration. This has allowed us to characterize protein-salt thermodynamic interactions.
We have observed the presence of large common-ion effects by examining the dependence of the diffusion
coefficients on salt concentration. Our results are compared to those previously reported for the lysozyme-
MgCl2-water ternary system. We have found that the common-ion effect is essentially the same for both salt
cases. On the other hand, by examining the dependence of the preferential-interaction coefficient on salt
concentration, we have found that salt preferentially interacts with the protein in the lysozyme-CaCl2-
water system, whereas water preferentially interacts with the protein in lysozyme-MgCl2-water system.
This is consistent with the known generally larger affinity of Mg2+
for water, as compared to Ca2+
, and the
different roles that these two divalent metal ions play in biochemical processes. We remark that neglecting

  

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

 

Collections: Chemistry