Effect of Chaotropic Reagents on Bovine Serum Albumin (BSA) - A Fluorescence Study

Abstract

The comparative study of the chemical denaturation by Chaotropic reagents urea and guanidine hydrochloride was studied on the model protein Bovine Serum Albumin (BSA) using UV-Vis Spectrophotometry and Steady State Fluorescence Spectroscopy. The denaturation or unfolding is a complex process for water soluble globular protein BSA as it contains multi – domains in which each domain can unfold dependently or independently and the association of different domains in the whole protein through various short range and long range interactions may affect the overall process. In the present experimental study the intrinsic fluorescence of amino acid (phenylalanine , tyrosine , tryptophan ) was explored to account for the denaturation process. The Chaotropic reagents of interest i.e. urea and guanidine hydrochloride being less polar than water, act upon by leading to an energetically unfavourable disruption of water structure. The addition of these denaturing agents to aqueous solutions therefore results in an increase in solvent-accessible surface area which destabilises hydrophobic aggregates, micelles and native protein structures ultimately leading to the process of unfolding or denaturation. Absorption studies were not effective in providing much information regarding the denaturation or unfolding of BSA. But the fluorescence emission spectra obtained describes successfully accounting for the changes during the unfolding and reasons behind it. The fluorescence intensity and anisotropy values well complemented each other for assigning the microenvironment of tryptophan to account for the changes during the unfolding of BSA. Guanidine hydrochloride has stronger chaotropic property than urea. It was experimentally observed that for the denaturation of BSA, less amount of guanidine hydrochloride 4 M is required for complete denaturation where as it is 8 M for urea.