Characteristics of tripeptide transport in human jejunal brush-border membrane vesicles.
These studies are aimed at characterizing the transport of the tripeptide, glycylglycyl-L-proline (GlyGlyPro) across human jejunal brush-border membrane vesicles. GlyGlyPro (0.65 mM) was hydrolyzed by brush-border membrane vesicles with the extent of hydrolysis per mg protein being 23% at 0.5 min, 57% at 1 min and complete hydrolysis at 60 min. Treatment of the membrane vesicles with gel-complexed papain (to remove membrane peptidases) resulted in minimal hydrolysis of GlyGlyPro up to 10 min of incubation. Measurement of GlyGlyPro influx with papain-treated vesicles in the presence of increasing medium osmolarity showed that uptake occurred into an osmotically reactive intravesicular space. Transport of GlyGlyPro with normal and papain-treated membrane vesicles was similar in the presence of an inward Na+ or K+ gradient. No overshoot phenomenon was observed in the presence of an inward proton gradient (extravesicular pH 5.5; intravesicular pH 7.5). An interior negative membrane potential induced by a K+ diffusion potential in the presence of valinomycin stimulated the uptake of the peptide. The effect of increasing concentrations on initial rates of GlyGlyPro uptake revealed the presence of a saturable component as well as a diffusional component. Preloading the membrane vesicles with 20 mM glycylsarcosylsarcosine stimulated uptake by 4-fold. Uptake of GlyGlyPro was inhibited greater than 50% by dipeptides and tripeptides and less than 15% by free amino acids. These results indicate that GlyGlyPro uptake in jejunal brush-border membrane vesicles is not energized by a Na+ or proton gradient and that transport occurs by carrier-mediated and diffusional processes.
Wilson
D
D
Gastroenterology Section, Zablocki Veterans Administration Medical Center, Milwaukee, WI.
Barry
J A
JA
Ramaswamy
K
K
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D004151:Dipeptides / Q000494:pharmacology; D006801:Humans; D007583:Jejunum / Q000378:metabolism*; D007700:Kinetics; D008081:Liposomes; D008563:Membrane Lipids / Q000378:metabolism; D008871:Microvilli / Q000187:drug effects / Q000378:metabolism*; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000378:metabolism* / Q000494:pharmacology; D010206:Papain
D000596:Amino Acids; D004151:Dipeptides; D008081:Liposomes; D008563:Membrane Lipids; D009842:Oligopeptides; C061903:glycyl-glycyl-proline; D010206:Papain