Kinetic evidence for a common transporter for glycylsarcosine and phenylalanylprolylalanine in renal brush-border membrane vesicles.

We investigated the interaction between glycylsarcosine (Gly-Sar), a neutral dipeptide, and phenylalanylprolylalanine (Phe-Pro-Ala), a neutral tripeptide, for transport into renal brush-border membrane vesicles isolated from Japanese F344 rats. This rat strain is genetically deficient in dipeptidylpeptidase IV. Owing to the absence of this enzyme, Phe-Pro-Ala was found to be completely resistant to hydrolysis by the brush-border membranes, and this enabled us to study the uptake of the intact tripeptide without interference by hydrolysis. Gly-Sar was also resistant to hydrolysis by these membrane preparations. Transport of Gly-Sar as well as that of Phe-Pro-Ala in these vesicles was driven by an inwardly directed H+ gradient. Gly-Sar transport was blocked completely by increasing concentrations of Phe-Pro-Ala and vice versa. Gly-Sar inhibited Phe-Pro-Ala transport competitively; and similarly, Phe-Pro-Ala inhibited Gly-Sar transport competitively. The dissociation constant (Kt) for Gly-Sar transport (94 +/- 5 microM) was very similar to the inhibition constant (Ki) for Gly-Sar to inhibit Phe-Pro-Ala transport (107 +/- 13 microM). The Kt for Phe-Pro-Ala transport (36 +/- 3 microM) was equal to the Ki for Phe-Pro-Ala to inhibit Gly-Sar transport (36 +/- 6 microM). Furthermore, linear correlation was exhibited by various neutral di- and tripeptides, which were also resistant to hydrolysis, in their abilities to inhibit the transport of Gly-Sar and that of Phe-Pro-Ala. These results strongly suggest that a common carrier system participates in the transport of neutral di- and tripeptides in renal brush-border membrane vesicles.