title: Modulation of the helical stability of a model peptide by ionic residues.
abstract: The mean residue ellipticity of the helical host peptide, acetyl-YEAAAKEAXAKEAAAKA-amide containing guest residues at position X, was measured as a function of pH and ionic strength at 0 degree C. Changes in ellipticity at 222 nm were interpreted in terms of a two-state helix/coil transition of a monomeric peptide. Variable pH measurements in low concentrations of KCl defined changes in helix stability resulting from the ionization of each guest residue. Variable [KCl] measurements at fixed pH generated ellipticity values for the neutral and ionic forms of each guest residue free of electrostatic and lyotropic contributions. These ellipticity values were used to calculate a helix propagation parameter for each form of a guest residue using the Lifson-Roig algorithm and assuming a universal nucleation parameter. In all cases, the propagation parameter of a residue is either unaffected or decreased by ionization of its side chain.
authors.affiliation: Department of Biochemistry, University of Iowa, Iowa City 52242.
authors.forename: S H
authors.initials: SH
authors.lastname: Park
authors.forename: W
authors.initials: W
authors.lastname: Shalongo
authors.forename: E
authors.initials: E
authors.lastname: Stellwagen
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D002942:Circular Dichroism; D006863:Hydrogen-Ion Concentration; D007477:Ions; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry* / Q000187:drug effects; D011189:Potassium Chloride / Q000494:pharmacology; D017433:Protein Structure, Secondary / Q000187:drug effects
chemical_list: D000596:Amino Acids; D007477:Ions; D010455:Peptides; D011189:Potassium Chloride