Yx. Pan et al., Expression of a cloned ovine gastrointestinal peptide transporter (oPepT1)in Xenopus oocytes induces uptake of oligopeptides in vitro, J NUTR, 131(4), 2001, pp. 1264-1270
We determined the primary structure, tissue distribution and in vitro funct
ional characterization of a peptide transporter, oPepT1, from ovine intesti
ne. Ovine PepT1 (oPepT1) cDNA was 2829-bp long, encoding a protein of 707 a
mino acid residues with an estimated molecular size of 78 kDa and an isoele
ctric point (pl) of 6.57. Transport function of oPepT1 was assessed by expr
essing oPepT1 in Xenopus oocytes using a two-electrode voltage-clamp techni
que. The transport process was electrogenic and pH dependent, but independe
nt of Na+, Cl- and Ca2+. The oPepT1 displayed a broad substrate specificity
for transport of neutral and charged dipeptides and tripeptides. All dipep
tides and tripeptides examined evoked inward currents in a saturable manner
, with an affinity constant (K-t) ranging from 27 mu mol/L to 3.0 mmol/L. N
o 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.