Native fluorescence and Mag-indo-1-protein interaction as tools for probing unfolding and refolding sequences of the bovine serum albumin subdomain in the presence of guanidine hydrochloride

Changes in the fluorescence spectrum of tryptophans Trp 134 and Trp 212 in bovine serum albumin (BSA) and of Trp 214 of human serum albumin in the pre sence of the chaotropic agent guanidine hydrochloride (Gnd) were studied. A detailed analysis of the fluorescence spectrum of native BSA yielded the f luorescence spectrum for each tryptophan of BSA. Modifications in the bindi ng of Mag-indo-1 to BSA, which results in a specific quenching of the fluor escence spectrum of Trp 134 associated with an energy transfer from Trp 134 to the protein-bound Mag-indo-1, were also investigated. Changes occurring when the Gnd concentration is decreased stepwise cover a larger concentrat ion scale of Gnd than the reverse protocol, allowing one to suggest that th e resulting conformational changes in the subdomain IA of BSA involve at le ast three different steps.