The peptides obtained from caseins selectively inhibited the enzymatic activities of prolyl-amino-peptidases, prolyl-amino- dipeptidases, and prolyl-endopeptidases in extracts of HT-29 and SW480 human colon carcinoma cells, but not in intact cells. They were not cytotoxic or growth inhibitory for these cells. Thus, the prolyl-rich selected peptides were good and selective inhibitors of MMPs and post-proline-cleaving proteases, demonstrating their potential to control inadequate proteolytic activity in the human digestive tract, without inducing cytotoxic effects. Table 1 IC50 values for inhibition by casein-derived peptides of prolyl-specific proteolytic activities extracted from HT-29 cells a
Protein
| Peptide code
| sequence
| IC50 ± SD (μM)
| Gly-Pro-AMC
| Z-Gly-Pro-AMC
| αs1-Casein
| Phe1
| FVAPFPEVFG
| 1500 ± 120
| 60 ± 5
| Phe2
| ENLLRFFVAPFPEVFG
| 1000 ± 85
| 30 ± 3 | Phe3
| NENLLRFFVAPFPEVFG
| 1500 ± 100
| 50 ± 3
| Phe4
| LNENLLRFFVAPFPEVFG
| 1500 ± 120
| 30 ± 4
| β-Casein
| Leu1
| NLHLPLPLL
| 1500 ± 150
| 150 ± 4
| Leu2
| ENLHLPLPLL
| 1900 ± 185
| 250 ± 15
| Leu3
| VENLHLPLPLL
| 1650 ± 145
| 250 ± 25
| a Residual enzyme activity determined using either Gly-Pro-AMC or Z-Gly-Pro-AMC as substrate in the presence of increasing concentrations of peptides, then IC50 were determined graphically, as the peptide concentration able to inhibit 50% of the enzyme activity.
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