title: Denaturation of proteins by SDS and tetraalkylammonium dodecyl sulfates.
abstract: This article describes the use of capillary electrophoresis (CE) to examine the influence of different cations (C(+); C(+) = Na(+) and tetra-n-alkylammonium, NR(4)(+), where R = Me, Et, Pr, and Bu) on the rates of denaturation of bovine carbonic anhydrase II (BCA) in the presence of anionic surfactant dodecylsulfate (DS(-)). An analysis of the denaturation of BCA in solutions of Na(+)DS(-) and NR(4)(+)DS(-) (in Tris-Gly buffer) indicated that the rates of formation of complexes of denatured BCA with DS(-) (BCA(D)-DS(-)(n,sat)) are indistinguishable and independent of the cation below the critical micellar concentration (cmc) and independent of the total concentration of DS(-) above the cmc. At concentrations of C(+)DS(-) above the cmc, BCA denatured at rates that depended on the cation; the rates decreased by a factor >10(4) in the order of Na(+) ≈ NMe(4)(+) > NEt(4)(+) > NPr(4)(+) > NBu(4)(+), which is the same order as the values of the cmc (which decrease from 4.0 mM for Na(+)DS(-) to 0.9 mM for NBu(4)(+)DS(-) in Tris-Gly buffer). The relationship between the cmc values and the rates of formation of BCA(D)-DS(-)(n,sat()) suggested that the kinetics of denaturation of BCA involve the association of this protein with monomeric DS(-) rather than with micelles of (C(+)DS(-))(n). A less-detailed survey of seven other proteins (α-lactalbumin, β-lactoglobulin A, β-lactoglobulin B, carboxypeptidase B, creatine phosphokinase, myoglobin, and ubiquitin) showed that the difference between Na(+)DS(-) and NR(4)(+)DS(-) observed with BCA was not general. Instead, the influence of NR(4)(+) on the association of DS(-) with these proteins depended on the protein. The selection of the cation contributed to the properties (including the composition, electrophoretic mobility, and partitioning behavior in aqueous two-phase systems) of aggregates of denatured protein and DS(-). These results suggest that the variation in the behavior of NR(4)(+)DS(-) with changes in R may be exploited in methods used to analyze and separate mixtures of proteins.
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts, USA.
authors.forename: Andrew
authors.initials: A
authors.lastname: Lee
authors.forename: Sindy K Y
authors.initials: SK
authors.lastname: Tang
authors.forename: Charles R
authors.initials: CR
authors.lastname: Mace
authors.forename: George M
authors.initials: GM
authors.lastname: Whitesides
mesh_terms: D000818:Animals; D024402:Carbonic Anhydrase II / Q000737:chemistry; D002417:Cattle; D007474:Ion Exchange; D007700:Kinetics; D008823:Micelles; D011489:Protein Denaturation / Q000187:drug effects*; D000644:Quaternary Ammonium Compounds / Q000737:chemistry / Q000494:pharmacology*; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry / Q000494:pharmacology*; D012996:Solutions; D013696:Temperature
chemical_list: D008823:Micelles; D000644:Quaternary Ammonium Compounds; D012996:Solutions; D012967:Sodium Dodecyl Sulfate; D024402:Carbonic Anhydrase II