Synthesis and characterization of a new and radiolabeled high-affinity substrate for H+/peptide cotransporters

FEBS J. 2007 Nov;274(22):5905-14. doi: 10.1111/j.1742-4658.2007.06113.x. Epub 2007 Oct 18.

Abstract

In this study we described the design, rational synthesis and functional characterization of a novel radiolabeled hydrolysis-resistant high-affinity substrate for H(+)/peptide cotransporters. L-4,4'-Biphenylalanyl-L-Proline (Bip-Pro) was synthesized according to standard procedures in peptide chemistry. The interaction of Bip-Pro with H(+)/peptide cotransporters was determined in intestinal Caco-2 cells constitutively expressing human H(+)/peptide cotransporter 1 (PEPT1) and in renal SKPT cells constitutively expressing rat H(+)/peptide cotransporter 2 (PEPT2). Bip-Pro inhibited the [(14)C]Gly-Sar uptake via PEPT1 and PEPT2 with exceptional high affinity (K(i) = 24 microm and 3.4 microm, respectively) in a competitive manner. By employing the two-electrode voltage clamp technique in Xenopus laevis oocytes expressing PEPT1 or PEPT2 it was found that Bip-Pro was transported by both peptide transporters although to a much lower extent than the reference substrate, Gly-Gln. Bip-Pro remained intact to > 98% for at least 8 h when incubated with intact cell monolayers. Bip-[(3)H]Pro uptake into SKPT cells was linear for up to 30 min and pH dependent with a maximum at extracellular pH 6.0. Uptake was strongly inhibited, not only by unlabeled Bip-Pro but also by known peptide transporter substrates such as dipeptides, cefadroxil, Ala-4-nitroanilide and delta-aminolevulinic acid, but not by glycine. Bip-Pro uptake in SKPT cells was saturable with a Michaelis-Menten constant (K(t)) of 7.6 microm and a maximal velocity (V(max)) of 1.1 nmol x 30 min(-1) x mg of protein(-1). Hence, the uptake of Bip-Pro by PEPT2 is a high-affinity, low-capacity process in comparison to the uptake of Gly-Sar. We conclude that Bip-[(3)H]Pro is a valuable substrate for both mechanistic and structural studies of H(+)/peptide transporter proteins.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Carrier Proteins / metabolism*
  • Cell Line
  • Chromatography, High Pressure Liquid
  • Female
  • Hydrogen / metabolism*
  • Kinetics
  • Patch-Clamp Techniques
  • Peptides / metabolism*
  • Radioisotopes*
  • Rats
  • Xenopus laevis

Substances

  • Carrier Proteins
  • Peptides
  • Radioisotopes
  • Hydrogen