title: Role of dipeptidyl peptidase IV in uptake of peptide nitrogen from beta-casomorphin in rabbit renal BBMV.
abstract: We examined the handling of radiolabeled beta-casomorphin, Tyr-Pro-[3H]Phe-Pro-Gly, by rabbit renal brush-border membrane vesicles (BBMV). The uptake of radiolabel into the vesicles was Na+-independent, but an inward-directed H+ gradient stimulated the uptake. The H+ gradient-dependent uptake was further accelerated by an interior-negative membrane potential, but inhibited in the presence of a protonophore. Treatment of the membrane vesicles with diisopropylfluorophosphate (DFP) greatly reduced the uptake of the radiolabel. Control as well as DFP-treated vesicles exhibited H+ gradient-dependent Gly-Sar uptake. Unlabeled beta-casomorphin inhibited Gly-Sar uptake in control vesicles, but the inhibition was significantly reduced in DFP-treated vesicles. DFP inhibited the activity of dipeptidyl peptidase IV in these vesicles and there was a direct correlation between the activity of the enzyme and the capacity of beta-casomorphin to inhibit Gly-Sar uptake. Many di- and tripeptides reduced the uptake of Gly-Sar and the uptake of radiolabel from beta-[3H]casomorphin to a similar extent. We conclude that beta-casomorphin is hydrolyzed by dipeptidyl peptidase IV and the products are transported into the vesicles by the H+ gradient-driven peptide transport system. This conclusion is supported by the results from the analysis of the incubation medium by high-performance liquid chromatography that showed rapid hydrolysis of the pentapeptide by brush-border membranes to di- and tripeptides.
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D018819:Dipeptidyl Peptidase 4; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases / Q000378:metabolism*; D004723:Endorphins / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007531:Isoflurophate / Q000494:pharmacology; D007672:Kidney Cortex / Q000378:metabolism*; D008564:Membrane Potentials; D008871:Microvilli / Q000378:metabolism; D009842:Oligopeptides / Q000378:metabolism*; D011188:Potassium / Q000502:physiology; D011817:Rabbits; D012964:Sodium / Q000502:physiology; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D004723:Endorphins; D009842:Oligopeptides; D007531:Isoflurophate; D014634:Valinomycin; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; C021968:beta-casomorphins; D012964:Sodium; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; D018819:Dipeptidyl Peptidase 4; D011188:Potassium