title: Ordered conformations of cationic polypeptides in anionic surfactant solutions.
abstract: Ionic poly(L-ornithine) at 45 degrees adopts a helical conformation in the presence of sodium dodecyl sulfonate or phosphate just as it is in sodium dodecyl sulfate solution as evidenced from circular dichroic spectra. But the polypeptide remains unordered in sodium tridecanate. Under similar conditions ionic poly(L-lysine) assumes the beta-form in all four anionic surfactant solutions. In sodium dodecyl phosphate solution at 45 degrees (Lys)n also undergoes a beta-to-helix transition in alkaline solution with a midpoint at pH 9.2, noting that dodecyl phosphoric acid has two dissociation constants with pKa of about 3 and 8. Raising the pH of the solution above 11 at 45 degrees converts the helical conformation back to the beta-form. This contrasts with a single beta-to-helix transition at pH 10.9 at 45 degrees for (Lys)n in sodium dodecyl sulfate solution.
mesh_terms: D000838:Anions; D002942:Circular Dichroism; D006863:Hydrogen-Ion Concentration; D010455:Peptides; D011107:Polylysine; D011487:Protein Conformation; D012967:Sodium Dodecyl Sulfate; D012996:Solutions
chemical_list: D000838:Anions; D010455:Peptides; D012996:Solutions; C008973:polyornithine; D011107:Polylysine; D012967:Sodium Dodecyl Sulfate