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TRANSPORTERS FROM HUMANS:
Transporter Information:
Name: solute carrier family 38, member 3
Symbol: SLC38A3
TC: 2.A.18.6.3
Locations: 3p21.3
Aliases: G17, SN1
GenBank: U49082
Swiss-Prot: Q99624
Accession Number: NM_006841
GDBGDB:9959038
LocusLink10991
OMIM604437
PubMed (10619430): Chaudhry FA, Reimer RJ, Krizaj D, Barber D, Storm-Mathisen J, Copenhagen DR,Edwards RH. Molecular analysis of system N suggests novel physiological roles in nitrogenmetabolism and synaptic transmission.Cell. 1999 Dec 23;99(7):769-80. PMID: 10619430 [PubMed - indexed for MEDLINE]

The amino acid glutamine has a central role in nitrogen metabolism. Although the molecular mechanisms responsible for its transport across cell membranes remain poorly understood, classical amino acid transport system N appears particularly important. Using intracellular pH measurements, we have now identified an orphan protein related to a vesicular neurotransmitter transporter as system N. Functional analysis shows that this protein (SN1) involves H+ exchange as well as Na+ cotransport and, under physiological conditions, mediates glutamine efflux as well as uptake. Together with the pattern of SN1 expression, these unusual properties suggest novel physiological roles for system N in nitrogen metabolism and synaptic transmission.

PubMed (10823827): Fei YJ, Sugawara M, Nakanishi T, Huang W, Wang H, Prasad PD, Leibach FH,Ganapathy V. Primary structure, genomic organization, and functional and electrogeniccharacteristics of human system N 1, a Na+- and H+-coupled glutaminetransporter.J Biol Chem. 2000 Aug 4;275(31):23707-17. PMID: 10823827 [PubMed - indexed for MEDLINE]

We have cloned the human Na(+)- and H(+)-coupled amino acid transport system N (hSN1) from HepG2 liver cells and investigated its functional characteristics. Human SN1 protein consists of 504 amino acids and shows high homology to rat SN1 and rat brain glutamine transporter (GlnT). When expressed in mammalian cells, the transport function of human SN1 could be demonstrated with glutamine as the substrate in the presence of LiCl (instead of NaCl) and cysteine. The transport activity was saturable, pH-sensitive, and specific for glutamine, histidine, asparagine, and alanine. Analysis of Li(+) activation kinetics showed a Li(+):glutamine stoichiometry of 2:1. When expressed in Xenopus laevis oocytes, the transport of glutamine or asparagine via human SN1 was associated with inward currents under voltage-clamped conditions. The transport function, monitored as glutamine- or asparagine-induced currents, was saturable, Na(+)-dependent, Li(+)-tolerant, and pH-sensitive. The transport cycle was associated with the involvement of more than one Na(+) ion. Uptake of asparagine was directly demonstrable in these oocytes by using radiolabeled substrate, and this uptake was inhibited by membrane depolarization. In addition, simultaneous measurement of asparagine influx and charge influx in the same oocyte yielded an asparagine:charge ratio of 1. These data suggest that SN1 mediates the influx of two Na(+) and one amino acid substrate per transport cycle coupled to the efflux of one H(+), rendering the transport process electrogenic.

>tr|Q99624 TRANSPORTER PROTEIN (NA+ AND H+ COUPLED AMINO ACID TRANSPORT SYSTEM N) - Homo sapiens (Human).
MEAPLQTEMVELVPNGKHSEGLLPVITPMAGNQRVEDPARSCMEGKSFLQKSPSKEPHFTDFEGKTSFGMSVFNLSNAIM
GSGILGLAYAMANTGIILFLFLLTAVALLSSYSIHLLLKSSGVVGIRAYEQLGYRAFGTPGKLAAALAITLQNIGAMSSY
LYIIKSELPLVIQTFLNLEEKTSDWYMNGNYLVILVSVTIILPLALMRQLGYLGYSSGFSLSCMVFFLIAVIYKKFHVPC
PLPPNFNNTTGNFSHVEIVKEKVQLQVEPEASAFCTPSYFTLNSQTAYTIPIMAFAFVCHPEVLPIYTELKDPSKKKMQH
ISNLSIAVMYIMYFLAALFGYLTFYNGVESELLHTYSKVDPFDVLILCVRVAVLTAVTLTVPIVLFPVRRAIQQMLFPNQ
EFSWLRHVLIAVGLLTCINLLVIFAPNILGIFGVIGATSAPFLIFIFPAIFYFRIMPTEKEPARSTPKILALCFAMLGFL
LMTMSLSFIIIDWASGTSRHGGNH