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Modified amino acids and peptides as substrates for the intestinal peptide transporter PepT1
- Meredith, David, Temple, Catherine S., Guha, Nishan, Sword, Corinna J., Boyd, C. A. Richard, Collier, Ian D., Morgan, Keith M., Bailey, Patrick D.
- European journal of biochemistry 2000 v.267 no.12 pp. 3723-3728
- Xenopus laevis, binding capacity, binding sites, dipeptides, histidine, mammals, models, peptide transporters, stereoisomers, tripeptides
- The binding affinities of a number of aminoâacid and peptide derivatives by the mammalian intestinal peptide transporter PepT1 were investigated, using the Xenopus laevis expression system. A series of blocked amino acids, namely NâacetylâPhe (AcâPhe), pheâamide (PheâNH2), NâacetylâPheâamide (AcâPheâNH2) and the parent compound Phe, was compared for efficacy in inhibiting the uptake of the peptide [3H]âdâPheâlâGln. In an equivalent set of experiments, the blocked peptides AcâPheâTyr, PheâTyrâNH2 and AcâPheâTyrâNH2 were compared with the parent compound PheâTyr. Comparing amino acids and derivatives, only AcâPhe was an effective inhibitor of peptide uptake (Kiâ=â1.81âÂ±â0.37âmm). AcâPheâNH2 had a very weak interaction with PepT1 (Kiâ=â16.8âÂ±â5.64âmm); neither Phe nor PheâNH2 interacted with PepT1 with measurable affinity. With the dipeptide and derivatives, unsurprisingly the highest affinity interaction was with PheâTyr (Kiâ=â0.10âÂ±â0.04âmm). The blocked Câterminal peptide PheâTyrâNH2 also interacted with PepT1 with a relatively high affinity (Kiâ=â0.94âÂ±â0.38âmm). Both AcâPheâTyr and AcâPheâTyrâNH2 interacted weakly with PepT1 (Kiâ=â8.41âÂ±â0.11 and 9.97âÂ±â4.01âmm, respectively). The results suggest that the Nâterminus is the primary binding site for both dipeptides and tripeptides. Additional experiments with four stereoisomers of AlaâAlaâAla support this conclusion, and lead us to propose that a histidine residue is involved in binding the Câterminus of dipeptides. In addition, a substrate binding model for PepT1 is proposed.