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 degrees 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.