title: Guanidinium chloride and urea denaturations of beta-lactoglobulin A at pH 2.0 and 25 degrees C: the equilibrium intermediate contains non-native structures (helix, tryptophan and hydrophobic patches).
abstract: We have carried out guanidinium chloride (GdmCl) and urea denaturations of bovine beta-lactoglobulin A (beta-lgA) at pH 2.0 and 25 degrees C, using far-UV and near-UV circular dichroism, near-UV absorption and tryptophan fluorescence spectroscopies. The stable intermediate state that occurs during GdmCl denaturation has been characterized by the far- and near-UV circular dichroism, tryptophan difference absorption, tryptophan fluorescence and 8-anilino-1-naphthalene sulphonic acid binding measurements. Following conclusions have been reached. (a) Urea-induced denaturation is not a two-state process. (b) GdmCl-induced denaturation is composed of two distinct two-state processes. (c) alpha-Helical content, burial of tryptophan residues and burial of hydrophobic surface area are more in the GdmCl-induced stable intermediate than those originally present in the native protein.
authors.affiliation: Department of Biosciences, Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia, Jamia Nagar, New Delhi-110 025, India.
authors.forename: Tanveer Ali
authors.initials: TA
authors.lastname: Dar
authors.forename: Laishram Rajendrakumar
authors.initials: LR
authors.lastname: Singh
authors.forename: Asimul
authors.initials: A
authors.lastname: Islam
authors.forename: Farah
authors.initials: F
authors.lastname: Anjum
authors.forename: Ali Akbar
authors.initials: AA
authors.lastname: Moosavi-Movahedi
authors.forename: Faizan
authors.initials: F
authors.lastname: Ahmad
mesh_terms: D000818:Animals; D002417:Cattle; D002942:Circular Dichroism; D019791:Guanidine / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007782:Lactoglobulins / Q000737:chemistry* / Q000378:metabolism; D010277:Parasympathomimetics / Q000494:pharmacology*; D011489:Protein Denaturation / Q000187:drug effects*; D017433:Protein Structure, Secondary; D013056:Spectrophotometry, Ultraviolet; D014364:Tryptophan / Q000737:chemistry*; D014508:Urea / Q000494:pharmacology*
chemical_list: D007782:Lactoglobulins; D010277:Parasympathomimetics; D014364:Tryptophan; D014508:Urea; D019791:Guanidine