AJP - Renal Physiology, Vol 252, Issue 4 670-F677, Copyright © 1987 by American Physiological Society
Role of dipeptidyl peptidase IV in uptake of peptide nitrogen from beta-casomorphin in rabbit renal BBMV
Y. Miyamoto, V. Ganapathy, A. Barlas, K. Neubert, A. Barth and F. H. Leibach
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.
