Transport of Charged Dipeptides by the Intestinal H+/Peptide Symporter PepT1 Expressed in Xenopus laevis Oocytes |
| |
Authors: | S Amasheh U Wenzel M Boll D Dorn W-M Weber W Clauss H Daniel |
| |
Institution: | (1) Institute of Nutritional Sciences, University of Giessen, Wilhelmstrasse 20, D-35392 Giessen, FRG, DE;(2) Institute of Animal Physiology, University of Giessen, Wartweg 95, D-35392 Giessen, FRG, DE |
| |
Abstract: | The cloned intestinal peptide transporter is capable of electrogenic H+-coupled cotransport of neutral di- and tripeptides and selected peptide mimetics. Since the mechanism by which PepT1 transports
substrates that carry a net negative or positive charge at neutral pH is poorly understood, we determined in Xenopus oocytes expressing PepT1 the characteristics of transport of differently charged glycylpeptides. Transport function of PepT1
was assessed by flux studies employing a radiolabeled dipeptide and by the two-electrode voltage-clamp-technique. Our studies
show, that the transporter is capable of translocating all substrates by an electrogenic process that follows Michaelis Menten
kinetics. Whereas the apparent K0.5 value of a zwitterionic substrate is only moderately affected by alterations in pH or membrane potential, K0.5 values of charged substrates are strongly dependent on both, pH and membrane potential. Whereas the affinity of the anionic
dipeptide increased dramatically by lowering the pH, a cationic substrate shows only a weak affinity for PepT1 at all pH values
(5.5–8.0). The driving force for uptake is provided mainly by the inside negative transmembrane electrical potential. In addition,
affinity for proton interaction with PepT1 was found to depend on membrane potential and proton binding subsequently affects
the substrate affinity. Furthermore, our studies suggest, that uptake of the zwitterionic form of a charged substrate contributes
to overall transport and that consequently the stoichiometry of the flux-coupling ratios for peptide: H+/H3O+ cotransport may vary depending on pH.
Received: 19 August 1996/Revised: 10 October 1996 |
| |
Keywords: | : Intestinal peptide transporter — Expression — Substrate specificity — Two-electrode voltage-clamp technique |
本文献已被 SpringerLink 等数据库收录! |
|