Thermodynamic parameters of the reversible isomerization of aspartic residues via a succinimide derivative

Abstract

Abstract Values of the thermodynamic quantities ΔH ° and ΔS ° for the reactions “Asp-peptide ⇆ Asupeptide ⇆ β-Asp-peptide” in aqueous solution have been obtained for the model peptides AcGlyXGlyGlyNHMe and AcXGlyNHMe (X  Asp, β-Asp, Asu; Asu = aminosuccinyl residue) from the temperature-dependence of equilibrium constants. The ΔH ° and ΔS ° values for the cyclization reactions of the carboxylic-acid form of the Asp and β-Asp side chains of the dipeptides and tetrapeptides are positive and coincident within experimental error. Medium values are 34 kJ mol −1 and 127 J K −1 mol −1 for ΔH ° and ΔS °, respectively. The molar enthalpies and molar entropies of the Asp-dipeptide and β-Asp-dipeptide, and of the Asp-tetrapeptide and β-Asp-tetrapeptide, did not exhibit significant differences.