Table 2.
Dipeptidyl peptidase IV (DPP-IV) half maximal inhibitory concentration (IC50), z-centered value of the hydrophobic parameter of side chains [v3 in the scale developed by Lin et al. (19)] of the amino acids constitutive of the peptides, and mode of inhibition of peptide analog of Ile-Pro-Ile.
| Set number | Peptide sequencea | z-Centered values ofv3 of the amino acids within the tripeptide | Predicted DPP-IV IC50 (μM) | Experimental DPP-IV IC50 (μM) | Mode of inhibition | Peptide hydrolyzed by DPP-IV | ||
|---|---|---|---|---|---|---|---|---|
| Xaa1 | Xaa2 | Xaa3 | ||||||
| 1 | IPI | 0.725 | 0.059 | 0.725 | 238 | 3.9 ± 1.0 | Competitive | NO |
| AIP | −0.194 | 0.725 | 0.059 | 103 | nd | nd | nd | |
| APA | −0.194 | 0.059 | −0.194 | 988 | 44.3 ± 3.2 | Competitive | NO | |
| APF | −0.194 | 0.059 | 0.716 | 168 | 65.8 ± 5.5 | Competitive | NO | |
| APR | −0.194 | 0.059 | −1.000 | 15 | 119.7 ± 3.5 | Competitive | NO | |
| ARP | −0.194 | −1.000 | 0.059 | 687 | nd | nd | nd | |
| IFK | 0.725 | 0.716 | −0.991 | 34 | nd | nd | nd | |
| IIF | 0.725 | 0.725 | 0.716 | 71 | nd | nd | nd | |
| IPA | 0.725 | 0.059 | −0.194 | 472 | 28.3 ± 3.4 | Competitive | NO | |
| IRF | 0.725 | −1.000 | 0.716 | 476 | nd | nd | nd | |
| IRK | 0.725 | −1.000 | −0.991 | 107 | nd | nd | nd | |
| KPA | −0.991 | 0.059 | −0.194 | 22,690 | 74.5 ± 7.0 | Competitive | NO | |
| KRI | −0.991 | −1.000 | 0.725 | 67,699 | nd | nd | nd | |
| RIF | −1.000 | 0.725 | 0.716 | 7,435 | nd | nd | nd | |
| RIR | −1.000 | 0.725 | −1.000 | 662 | nd | nd | nd | |
| RKR | −1.000 | −0.991 | −1.000 | 2,451 | nd | nd | nd | |
| 2 | FPF | 0.716 | 0.059 | 0.716 | 177 | 247.0 ± 32.7 | Competitive | YES |
| FPI | 0.716 | 0.059 | 0.725 | 524 | 45.2 ± 5.3 | Competitive | NO | |
| FPW | 0.716 | 0.059 | 1.000 | 67 | 54.9 ± 2.9 | Competitive | YES | |
| IAI | 0.725 | −0.194 | 0.725 | 97 | nd | nd | nd | |
| IPF | 0.725 | 0.059 | 0.716 | 80 | 47.3 ± 12.3 | Competitive | YES | |
| IPW | 0.725 | 0.059 | 1.000 | 31 | 175.3 ± 5.5 | Competitive | YES | |
| WPF | 1.000 | 0.059 | 0.716 | 214 | 159.8 ± 12.8 | Mixed-type | YES | |
| WPI | 1.000 | 0.059 | 0.725 | 633 | 133.0 ± 14.7 | Mixed-type | NO | |
| WPW | 1.000 | 0.059 | 1.000 | 81 | 120.1 ± 13.1 | Mixed-type | YES | |
aPeptide sequences abbreviated with the one letter amino acid code. The first set corresponds to Ile-Pro-Ile and its 15 associated peptide analogs. The second set corresponds to Ile-Ala-Ile and the eight additional peptides tested, which possess the Xaa1-Pro-Xaa3 structure, with Xaa1 and Xaa3 being Ile, Phe, or Trp.
nd, not determined; IC50, DPP-IV half maximal inhibitory concentration; NO, peptide not cleaved during incubation with DPP-IV; YES, peptide cleaved following incubation with DPP-IV.