Expression of a Cloned Ovine Gastrointestinal Peptide Transporter (oPepT1) in Xenopus Oocytes Induces Uptake of Oligopeptides in Vitro

We determined the primary structure, tissue distribution and in vitro functional characterization of a peptide transporter, oPepT1, from ovine intestine. Ovine PepT1 (oPepT1) cDNA was 2829-bp long, encoding a protein of 707 amino acid residues with an estimated molecular size of 78 kDa and an isoelectric point (pI) of 6.57. Transport function of oPepT1 was assessed by expressing oPepT1 in Xenopus oocytes using a two-electrode voltage-clamp technique. The transport process was electrogenic and pH dependent, but independent of Na+, Cl- and Ca2+. The oPepT1 displayed a broad substrate specificity for transport of neutral and charged dipeptides and tripeptides. All dipeptides and tripeptides examined evoked inward currents in a saturable manner, with an affinity constant (Kt) ranging from 27 micromol/L to 3.0 mmol/L. No responses were detected from tetrapeptides or free amino acids. Northern blot analysis demonstrated that oPepT1 was expressed in the small intestine, omasum and rumen, but was not expressed in liver and kidney. The presence of the peptide transporter in the forestomach at such levels could provide nutritionally important amino acid nitrogen to ruminants.