TRANSPORT OF AMINO-ACID ARYL AMIDES BY THE INTESTINAL H+ PEPTIDE COTRANSPORT SYSTEM, PEPT1/

Transport of amino acid aryl amides by the intestinal H+/peptide sympo rter (PEPT1) was studied in Caco-2 cells and in Xenopus laevis oocytes expressing human PEPT1. Several amino acid amides were able to inhibi t the uptake of [C-14]glycylsarcosine in Caco-2 cells. Ala-4-nitroanil ide (K-i = 0.08 mM), Phe-4-nitroanilide (K-i = 0.09 mM) and Ala-4-phen ylanilide (K-i = 0.03 mM) were accepted as substrates with equal or hi gher affinity than natural Ala-Xaa dipeptides. Ala-anilide (K-i = 2.9 mM), Ala-7-amido-4-methylcoumarin (K-i = 0.2 mM), Ala-4-chloroanilide (K-i = 0.3 mM) and Ala-4-methylanilide (K-i = 0.3 mM) were also recogn ized by PEPT1 as substrates. In contrast, alanine, Ala-amide, Phe-amid e, Ala-methyl ester, Ala-4-nitrobenzyl ester and Ala-methylamide were not recognized (K-i > 20 mM). In X. laevis oocytes, transport of Ala-4 -nitroanilide, Ala-7-amido-4-methylcoumarin, Ala-4-methylanilide and A la-anilide was associated with transfer of positive charge and the cur rents were saturable with respect to substrate concentration (K-0.5 va lues: 0.1, 0.2, 0.8 and 3.1 mM, respectively). The currents induced by Ala-4-methylanilide were saturable with respect to the substrate conc entration and influenced by the membrane potential. The affinity of th e transporter for Ala-4-methylanilide was also found to be influenced by the membrane potential. We conclude that the intestinal H+/peptide cotransport system PEPT1 accepts amino acid aryl amides as substrates.