DYNAMIC LIGHT SCATTERING: A USEFUL OPTICAL METHOD TO PROBE COMMON-ION EFFECTS IN PROTEIN-SALT AQUEOUS SOLUTIONS

2005 
We report measurements of protein diffusion coefficients for lysozyme aqueous solutions using dynamic light scattering (DLS). DLS measurements were performed on the buffer-free lysozyme-NaCl-water and lysozyme-Na2SO4-water ternary systems at pH 4.5 and 25 oC. The dependence of lysozyme diffusion coefficients as a function of salt concentration is analyzed. We find that the behavior of the protein diffusion coefficient in the presence of Na2SO4 is significantly different from that in the presence of NaCl. Our DLS measurements show that the common-ion effect plays an important role in the case of lysozyme-NaCl solutions but not in the case of lysozyme-Na2SO4 solutions. Therefore DLS is a useful optical method that can be used to probe the presence of common-ion effects in protein-salt aqueous solutions.
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