Characteristics of L-glutamine transport in equine jejunal brush border membrane vesicles

Rabih M. Salloum From the Departments of Surgery (Salloum, Souba) and Immunology and Medical Microbiology (Duckworth), College of Medicine and the Department of Large Animal Clinical Sciences (Madison), College of Veterinary Medicine, University of Florida, Gainesville, FL 32610.

Search for other papers by Rabih M. Salloum in
Current site
Google Scholar
PubMed
Close
 MD
,
Donna Duckworth From the Departments of Surgery (Salloum, Souba) and Immunology and Medical Microbiology (Duckworth), College of Medicine and the Department of Large Animal Clinical Sciences (Madison), College of Veterinary Medicine, University of Florida, Gainesville, FL 32610.

Search for other papers by Donna Duckworth in
Current site
Google Scholar
PubMed
Close
 PhD
,
John B. Madison From the Departments of Surgery (Salloum, Souba) and Immunology and Medical Microbiology (Duckworth), College of Medicine and the Department of Large Animal Clinical Sciences (Madison), College of Veterinary Medicine, University of Florida, Gainesville, FL 32610.

Search for other papers by John B. Madison in
Current site
Google Scholar
PubMed
Close
 VMD
, and
Wiley W. Souba From the Departments of Surgery (Salloum, Souba) and Immunology and Medical Microbiology (Duckworth), College of Medicine and the Department of Large Animal Clinical Sciences (Madison), College of Veterinary Medicine, University of Florida, Gainesville, FL 32610.

Search for other papers by Wiley W. Souba in
Current site
Google Scholar
PubMed
Close
 MD, ScD

Click on author name to view affiliation information

SUMMARY

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 μM and 5 mM revealed a single saturable high-affinity carrier with a Michaelis constant of 519 ± 90 μM/ 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 μM 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.

SUMMARY

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 μM and 5 mM revealed a single saturable high-affinity carrier with a Michaelis constant of 519 ± 90 μM/ 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 μM 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.

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 35 35 5
PDF Downloads 20 20 2
Advertisement