title: Substrate-specificity of glutamine transporters in membrane vesicles from rat liver and skeletal muscle investigated using amino acid analogues.
abstract: We investigated the effects of glutamine and histidine analogues on glutamine transport processes in membrane vesicles prepared from rat liver (sinusoidal membrane) and skeletal muscle (sarcolemma). L-[14C]Glutamine is transported in these membranes predominantly by Systems N/Nm (liver and muscle respectively), and to a lesser extent by Systems A and L (e.g. about 60, 20 and 20% of total flux respectively via Systems N, A and L at 0.05 mM-glutamine in liver membrane vesicles). The glutamine anti-metabolites 6-diazo-5-oxo-L-norleucine and acivicin were relatively poor inhibitors of glutamine uptake into liver membrane vesicles (less than 25% inhibition at 20-fold excess) and appeared primarily to inhibit System A activity (i.e. N-methylaminoisobutyric acid-inhibitable glutamine uptake). In similar experiments azaserine (also a glutamine anti-metabolite) inhibited approx. 50% of glutamine uptake, apparently by inhibition of System A and also of System L (i.e. 2-amino-2-carboxybicyclo[2,2,1]heptane-inhibitable glutamine uptake). Glutamate gamma-hydroxamate, aspartate beta-hydroxamate, histidine and N'-methylhistidine were all strong inhibitors of glutamine uptake into liver membrane vesicles (greater than 65% inhibition at 20-fold excess), but neither homoglutamine nor N'-methylhistidine produced inhibition. L-Glutamate-gamma-hydroxamate was shown to be a competitive inhibitor of glutamine transport via System N (Ki approximately 0.6 mM). Glutamine uptake in sarcolemmal vesicles showed a similar general pattern of inhibition as in liver membrane vesicles. The results highlight limits on the substrate tolerance of System N; we suggest that the presence of both an L-alpha-amino acid group and a nitrogen group with a delocalized lone-pair of electrons (amide or pyrrole type), separated by a specific intramolecular distance (C2-C4 chain equivalent), is important for substrate recognition by this transporter.
authors.affiliation: Department of Anatomy and Physiology, University of Dundee, Scotland, U.K.
authors.forename: S Y
authors.initials: SY
authors.lastname: Low
authors.forename: P M
authors.initials: PM
authors.lastname: Taylor
authors.forename: A
authors.initials: A
authors.lastname: Ahmed
authors.forename: C I
authors.initials: CI
authors.lastname: Pogson
authors.forename: M J
authors.initials: MJ
authors.lastname: Rennie
mesh_terms: D000596:Amino Acids / Q000494:pharmacology; D000598:Amino Acids, Cyclic; D000621:Aminoisobutyric Acids / Q000494:pharmacology; D000818:Animals; D001377:Azaserine / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D003980:Diazooxonorleucine / Q000494:pharmacology; D005260:Female; D005973:Glutamine / Q000378:metabolism; D007700:Kinetics; D008094:Lithium / Q000494:pharmacology; D008099:Liver / Q000378:metabolism*; D009132:Muscles / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012508:Sarcolemma / Q000378:metabolism; D012964:Sodium / Q000494:pharmacology
chemical_list: D000596:Amino Acids; D000598:Amino Acids, Cyclic; D000621:Aminoisobutyric Acids; D002352:Carrier Proteins; C037853:glutamine transport proteins; D003980:Diazooxonorleucine; D005973:Glutamine; C006504:2-aminobicyclo(2,2,1)heptane-2-carboxylic acid; C017911:2-(methylamino)isobutyric acid; D001377:Azaserine; D008094:Lithium; D012964:Sodium