Stability of peptide AHEPVK against gastrointestinal enzymes observed by SEC chromatograms. Separation was performed on a Biosep SEC-S2000 column (300 × 7.8 mm). Mobile phase consisted of 45% acetonitrile containing 0.1% TFA eluted at a flow rate of 1.0 ml/min. Peptide was eluted as peak at retention time illustrated in the box. A: Pure peptide; B: The peptide solution (0.1 mg/ml) was incubated in buffer solutions (control); C: The peptide solution was incubated with 0.05% pepsin solution for 2.5 hrs at 37°C; D: The peptide solution was successively digested with pepsin for 2.5 hrs. They were further incubated in pancreatin solution for another 2.5 hrs at 37°C.