Characteristics of L-glutamine transport in equine jejunal brush border membrane vesicles.
The sodium-dependent transporter system responsible for L-glutamine uptake by brush border membrane vesicles prepared from equine jejunum was characterized. Vesicle purity was ascertained by a 14- to 17-fold increase in activity of the brush border enzyme markers. Glutamine uptake was found to occur into an osmotically active space with negligible membrane binding. The sodium-dependent velocity represented approximately 80% of total uptake and demonstrated overshoots. Kinetic studies of sodium-dependent glutamine transport at concentrations between 5 microM and 5 mM revealed a single saturable high-affinity carrier with a Michaelis constant of 519 +/- 90 microM and a maximal transport velocity of 3.08 +/- 0.97 nmol/mg of protein/10 s. Glutamine uptake was not affected by changes in environmental pH. Lithium could not substitute for sodium as a contransporter ion. 2-Methylaminoisobutyric acid inhibited the sodium-dependent carrier only minimally, but marked inhibition (> 90%) was observed in the presence of histidine, alanine, cysteine, and nonradioactive glutamine. Kinetic analysis of the sodium-independent transporter revealed it to have a Michaelis constant = 260 +/- 47 microM and a maximal transport velocity of 0.32 +/- 0.06 nmol/mg of protein/10 s. We conclude that glutamine transport in equine jejunal brush border membrane vesicles occurs primarily via the system B transporter and, to a lesser extent, by a sodium-independent carrier.
Salloum
R M
RM
Department of Surgery, College of Medicine, University of Florida, Gainesville 32610.
Duckworth
D
D
Madison
J B
JB
Souba
W W
WW
D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002412:Cations / Q000494:pharmacology; D005973:Glutamine / Q000493:pharmacokinetics*; D006736:Horses / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007408:Intestinal Absorption / Q000187:drug effects / Q000502:physiology; D007583:Jejunum / Q000378:metabolism*; D008871:Microvilli / Q000378:metabolism; D008954:Models, Biological; D011188:Potassium / Q000502:physiology; D012964:Sodium / Q000502:physiology
D000596:Amino Acids; D002412:Cations; D005973:Glutamine; D012964:Sodium; D011188:Potassium