| Abstract
| - Dipeptide transporters in small intestine have a very wide substrate specificity, so that the transportersometimes serves as a carrier for peptide-like compounds. We have synthesized dipeptide analoguesconjugated at an ε-amino group of Lys in Val-Lys or Lys-Sar with fluorescent compounds such asfluorescein isothiocyanate and coumarin-3-carboxylic acid. Uptakes of these peptide analogues wereexamined by measuring intracellular accumulations into monolayers of the human intestinal epithelialcell line Caco-2 expressing the dipeptide transporter PEPT1. Kinetic analysis and effects of additioneither of uncoupler (protonophore) or by Gly-Sar, one of the good substrates of PEPT1, revealed thatfluorescent dipeptides were taken up by passive diffusion. In contrast, these analogues remarkablyinhibited the Gly-Sar uptake by Caco-2 cells. Among the fluorescent analogues synthesized in thispaper, Val-Lys(Flu) was the most potent competitive inhibitor against the Gly-Sar uptake with aninhibition constant of 5 μM. This value is the smallest among those ever reported: Val-Lys(Flu) hasthe highest affinity for PEPT1 among chemicals ever reported. The importance of the hydrophobicpart of the substrate was pointed out.
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