title: Conformational transition of insulin induced by n-alkyltrimethylammonium bromides in aqueous solution.
abstract: A surfactant-induced conformational transition of bovine insulin has been detected by difference spectroscopy for a homologous series of n-alkytrimethylammonium bromides, chain length C10-C16 at pH 10.0, 25 degrees C. The transition was followed as a function of surfactant concentration by absorbance measurements at 275 nm and the data were analysed to obtain the Gibbs energy of the transition in water (delta Gw degree) and in a hydrophobic environment (delta Ghc degree) for saturated protein-surfactant complexes. A value of delta Gw degree of -11.8 +/- 1.8 kJ mol-1 was found independent of n-alkyl chain length, which is similar to the value found for the n-alkylsulfate-induced transition in a previous study (-14.6 +/- 3.0 kJ mol-1). The values of delta Ghc degree were in the range approximately -88 to -100 kJ mol-1 for chain lengths from C10 to C16. The values of delta Ghc degree vs. chain length for both the n-alkyltrimethylammonium bromides and the n-alkylsulfates lie on the same curve, demonstrating that delta Ghc degree is independent of the nature of the surfactant head group.
authors.affiliation: Departamento de Fisica Aplicada, Universidade de Santiago de Compostela, Galicia, Spain.
authors.forename: C
authors.initials: C
authors.lastname: Pombo
authors.forename: G
authors.initials: G
authors.lastname: Prieto
authors.forename: J M
authors.initials: JM
authors.lastname: del Río
authors.forename: F
authors.initials: F
authors.lastname: Sarmiento
authors.forename: M N
authors.initials: MN
authors.lastname: Jones
mesh_terms: D001965:Bromides / Q000737:chemistry; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D007328:Insulin / Q000737:chemistry*; D011487:Protein Conformation; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D012996:Solutions; D013057:Spectrum Analysis / Q000379:methods; D013501:Surface-Active Agents / Q000737:chemistry*; D013816:Thermodynamics; D014867:Water
chemical_list: D001965:Bromides; D007328:Insulin; D000644:Quaternary Ammonium Compounds; D012996:Solutions; D013501:Surface-Active Agents; D014867:Water