Factors affecting cleavage at aspartic residues in model decapeptides

The aqueous stability of four decapeptides was investigated in an acetate buffer at different pHs (4.0–5.5) and temperatures (25, 40, and 60 °C). The four decapeptides share the following common sequence—Tyr-Ala-Arg-Asp-Aaa-Pro-Leu-Gly-Tyr-Thr, where Aaa represents Gln, Pro, Lys, or Leu. The major degradation pathway was found to be the cleavage at Asp-Aaa. The degradation process fits well the first-order kinetics. The cleavage of the decapeptide containing Asp-Pro was faster than that of other three decapeptides. A strong pH dependence of cleavage was observed for all decapeptides, especially when pH was <5. Three out of four decapeptides showed a clear Arrhenius temperature dependency whereas Asp-Pro-containing peptide did not.