Elucidating the mode of action of urea on mammalian serum albumins and protective effect of sodium dodecyl sulfate

The effect of sodium dodecyl sulfate (SDS) on human, bovine, porcine, rabbit and sheep serum albumins were investigated at pH 3.5 by using various spectroscopic techniques like circular dichroism (CD), intrinsic fluorescence and dynamic light scattering (DLS). In the presence of 4.0 mM SDS the secondary structure of all the albumins were not affected as measured by CD but fluorescence spectra revealed 8.0 nm blue shift in emission maxima. We further checked the stability of albumins in the absence and presence of 4.0 mM SDS by urea and temperature at pH 3.5. In the absence of SDS, urea starts unfolding both secondary as well as tertiary structural elements of the all the albumins at ∼2.0 M urea but in the presence of 4.0 mM SDS, urea was unable to unfold even up to 9.0 M. The albumins were thermally less stable at pH 3.5 with decrease in Tm but in the presence of 4.0 mM SDS, the Tm was increased. From this study, it was concluded that SDS is showing a protective effect against urea as well as thermal denaturation of albumins. This behavior may be due to electrostatic as well as the hydrophobic interaction of SDS with albumins. Further, we have proposed the mechanism of action of urea. It was found that urea interacted with proteins directly when proteins are in charged form. Indirect interaction may be taking place when the environment is more hydrophobic.