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 ID: 10619430 RIS Download
Mesh terms: Amino Acid Sequence | Amino Acid Transport Systems, Neutral | Animals | Astrocytes | Brain | Carrier Proteins | Cell Line | Cloning, Molecular | Glutamine | Humans | Hydrogen-Ion Concentration | Immunohistochemistry | Membrane Proteins | Membrane Transport Proteins | Molecular Sequence Data | Neurotransmitter Agents | Nitrogen | Organ Specificity | Rats | Sequence Alignment | Sodium | Synapses | Synaptic Transmission
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