SELECTIVE EFFECT OF ZINC ON UPHILL TRANSPORT OF OLIGOPEPTIDES INTO KIDNEY BRUSH-BORDER MEMBRANE-VESICLES

Based on the involvement of zinc in hydrolysis of peptides, we hypothesized that Zn2+ may also play a role in peptide transport. To investigate this hypothesis, kidney brush border membrane vesicles (BBMV) were incubated for 30 min with different concentrations of ZnSO4 before use in uptake studies. This incubation increased by twofold the overshoot uptake of H-3-Gly-L-Gln, D-Leu-I-125-Tyr and H-3-cephalexin (all high-affinity substrates for the oligopeptide/H+ symporter) without affecting passive and/or facilitated diffusion of these substrates. Zinc had no effect on the uptake of either glutamine or glucose by kidney BBMV. Among a group of metal ions (cobalt, iron, copper, cadmium, and manganese), only manganese and copper substantially stimulated the activity of the oligopeptide/H+ symporter. DTPA (a complexing agent) inhibited dipeptide uptake, which was reversed by the addition of zinc to the BBMV. Zinc treatment of BBMV reduced the EC(50) value of inhibition of H-3-Gly-L-Gln uptake by unlabeled Gly-L-Gln by twofold (90 +/- 8 vs. 45 +/- 4 mu M). Similarly, zinc treatment of BBMV reduced the EC(50) value for inhibition of D-Leu-I-125-Tyr uptake by bestatin from 80 +/- 4 to 40 +/- 3 mM. In conclusion, the data show that zinc has a selective effect on transport of nutrients into kidney BBMV. It stimulates uphill transport of oligopeptides by a modification of their affinity for the binding site of the membrane transporter.