title: Sodium dodecyl sulfate promoting a cooperative association process of sodium cholate with bovine serum albumin.
abstract: Sodium cholate (NaC) was used as a representative bile salt in the process of cooperative binding to bovine serum albumin (BSA) in a mixture with sodium dodecyl sulfate (SDS). The experiments were performed in 0.02 M Tris-HCl buffer solution (pH 7.50), in the presence of 0.1% BSA and at 25 degrees C. The aim of this study is to provide information on the performance of the BSA in the promotion of cooperative binding of sodium cholate promoted by the presence of SDS. The method used to monitor the binding was based on the analysis of the effect of SDS and NaC concentrations and their mixtures upon the fluorescence intensity of the BSA tryptophan residues. Plots of the fluorescence emission bands in terms of the A0/A ratio vs surfactant concentrations, where A0 and A represent the areas of emission bands in the presence and absence of the surfactants, respectively, were drawn in order to investigate the surfactant interaction with the protein. An alternative methodology, the specific conductivity vs surfactant concentration plots, was used, which involves mixtures of SDS and NaC to investigate the association processes, through the determination of the critical aggregation concentration (cac, when in the presence of protein) and the critical micellar concentration (cmc). The results led to a general conclusion that as the mixed micellar aggregates become richer in the bile salt monomer, the tendency to lose the reactivity with the protein increases. According to our results, a clear evidence of the predomination of BSA-SDS-NaC complexes is found only for the SDS molar fraction above approximately 0.6, and below this fraction a tendency toward free mixed micelles starts to predominate.
authors.affiliation: Departamento de Química da Universidade Federal de Santa Catarina, CEP: 88040-900, Florianópolis, SC, Brazil.
authors.forename: Bianca
authors.initials: B
authors.lastname: Schweitzer
authors.forename: Arlindo C
authors.initials: AC
authors.lastname: Felippe
authors.forename: Alexandre
authors.initials: A
authors.lastname: Dal Bó
authors.forename: Edson
authors.initials: E
authors.lastname: Minatti
authors.forename: Dino
authors.initials: D
authors.lastname: Zanette
authors.forename: Antonio
authors.initials: A
authors.lastname: Lopes
mesh_terms: D000818:Animals; D002417:Cattle; D006358:Hot Temperature; D008823:Micelles; D011485:Protein Binding; D012710:Serum Albumin, Bovine / Q000737:chemistry*; D020358:Sodium Cholate / Q000737:chemistry*; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013501:Surface-Active Agents / Q000737:chemistry*; D014364:Tryptophan / Q000737:chemistry*
chemical_list: D008823:Micelles; D013501:Surface-Active Agents; D012710:Serum Albumin, Bovine; D012967:Sodium Dodecyl Sulfate; D014364:Tryptophan; D020358:Sodium Cholate