Characteristics of glutamine transport in dog jejunal brush-border membrane vesicles.
The present study characterizes glutamine transport across brush-border membrane vesicles (BBMV) prepared from dog jejunum. The purity of these vesicles was demonstrated by a 20-fold enrichment of leucine aminopeptidase, a marker for BBM. Glutamine uptake was found to occur into an osmotically active space with no membrane binding and to exhibit temperature and pH dependence (optimal uptake at pH 7-7.5). Glutamine uptake was driven by an inwardly directed Na+ gradient with a distinct overshoot not observed under K+ gradient. Lithium could not substitute for Na+ as a stimulator of glutamine uptake. Na+-dependent glutamine uptake was not inhibited by methylaminoisobutyric acid, a typical substrate for system A, and was found to be electrogenic and saturable with a Km of 0.97 +/- 0.58 mM and a Vmax of 3.93 +/- 0.99 nmol.mg protein-1.10 s-1. A Na+-glutamine coupling ratio of 1:1 could be demonstrated by a plot of Hill transformation. Na+-independent glutamine uptake was found to be electroneutral and saturable with a Km of 3.70 +/- 0.66 mM and a Vmax of 2.70 +/- 1.55 nmol.mg protein-1.10 s-1. Inhibition studies confirmed the presence of a Na+-dependent as well as a Na+-independent carrier for glutamine uptake. We conclude that glutamine uptake across dog BBMV occurs via two transport systems: a Na+-dependent high-affinity system similar to the neutral brush-border system and a Na+-independent lower-affinity system similar to system L.
Bulus
N M
NM
Department of Surgery, Vanderbilt University, Nashville, Tennessee 37232.
Abumrad
N N
NN
Ghishan
F K
FK
D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002412:Cations; D002794:Choline / Q000494:pharmacology; D004285:Dogs; D005973:Glutamine / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007583:Jejunum / Q000378:metabolism* / Q000648:ultrastructure; D007700:Kinetics; D008094:Lithium / Q000494:pharmacology; D008564:Membrane Potentials; D008871:Microvilli / Q000378:metabolism; D009994:Osmolar Concentration; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology; D013696:Temperature
D000596:Amino Acids; D002412:Cations; D005973:Glutamine; D008094:Lithium; D012964:Sodium; D002794:Choline; D011188:Potassium