Salt-Specific Effects in Solutions of Human Serum Albumin: Small-Angle X-Ray Scattering and Osmometry
Jaka Marušič, Jurij Reščič, Andrej Jamnik and Matija Tomšič*
University of Ljubljana, Faculty of Chemistry and Chemical Technology,
Aškerčeva 5, SI-1000 Ljubljana, Slovenia
* Corresponding author: E-mail:
Matija.Tomsic@fkkt.uni-lj.si
Abstract
Small-angle X-ray scattering (SAXS) method and membrane osmometry were used to
study salt-specific effects of various 1:1 salts at pH 4.0 and 8.0 on
interparticle interactions and thermodynamic quantities in aqueous solutions of
human serum albumin (HSA) at 25 °C. Our results show that Donnan pressures of
HSA solutions exhibit stronger dependence on the type of anion than on the type
of cation in the solution. However, the presence of different salts in the HSA
solutions only weakly affects the SAXS curves in the accessible q
regime (0.1 nm–1 < q < 7 nm–1). SAXS data were
analyzed utilizing generalized indirect Fourier transformation, which indicated
weak repulsive interactions between HSA molecules in all cases. Further, this
analysis of the experimental SAXS curves strongly suggests that HSA molecules in
the studied solutions have the shape of oblate ellipsoid with dimensions of
approximately 8.5 × 8.5 × 4 nm. Both SAXS and membrane osmometry results can be
satisfactorily explained in terms of the strength of the inter-particle
interactions and conform to the trends of the Hofmeister series.
Keywords: Human serum albumin, osmotic coefficient, small-angle X-ray scattering, indirect fourier transformation, Hofmeister series.