Characterization of an oligopeptide transporter in renal lysosomes

Renal lysosomes play a major role in catabolism of plasma proteins. Final p roducts of this catabolism include dipeptides and tripeptides that must be exported to the cytosol for hydrolysis. The aim of the present study was to determine whether an oligopeptide transporter is present in the renal lyso somal membrane that could mediate this export. The existence of an oligopep tide transporter was probed with the uptake of glycylglutamine (Gly-Gln) by membrane vesicles prepared from renal lysosomes, Kinetic analysis showed t he presence of a single transporter with a K-m of 8.77 mM for the uptake of Gly-Gln. The Gly-Gln uptake was energized by the imposition of an inwardly directed proton gradient (pH(out) 5.0/pH(in) 7.3) and membrane potential ( outside positive/inside negative) resulting in overshoot. The Gly-Gln uptak e was inhibited by the presence of dipeptides and tripeptides, but not amin o acids. Western blot analysis of lysosomal membrane proteins with Pept-1 ( an oligopeptide transporter) antibody as the probe showed the presence of a n immunoreactive protein. This immunoreaction was abolished when the antise rum was preabsorbed with the Pept-1 epitope (0.5 yg/ml). In conclusion, the present data show the existence of a low-affinity dipeptide transporter in the renal lysosomal membrane that appears to belong to the Pept family of transporters. The function of this transporter appears to be to prevent acc umulation of dipeptides in renal lysosomes. (C) 2000 Elsevier Science B.V. All rights reserved.