ACE-inhibitory activity and structural properties of peptide Asp-Lys-Ile-His-Pro [beta-CN f(47-51)]. Study of the peptide forms synthesized by different methods.

Some of the most potent ACE-inhibitory peptides described in food have a proline at the end of their sequence, a characteristic that can cause problems in the synthesis procedures. In this work, we studied two different preparations of peptide Asp-Lys-Ile-His-Pro (DKIHP), which were obtained by two different synthetic procedures (Boc and Fmoc). The peptide synthesized by the Boc method yielded a unique conformer, containing trans-Pro, and significant ACE-inhibitory activity (IC(50) = 113.18 microM). The chromatographic and NMR data of this active conformer are reported. The peptide synthesized by Fmoc chemistry yielded three conformers, two of them containing trans-Pro and a third one containing cis-Pro, and showed a lower activity (IC(50) = 577.92 microM). This was attributed to the presence of conformers with less (or none) activity. We have pointed out the importance of performing structural studies on these type of peptides before testing their ACE-inhibitory activity.