Abstract
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.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Amino Acid Sequence
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Amino Acid Transport Systems, Neutral*
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Animals
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Astrocytes / metabolism
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Astrocytes / ultrastructure
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Brain / metabolism
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Brain / ultrastructure
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Carrier Proteins / genetics
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Carrier Proteins / metabolism*
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Cell Line
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Cloning, Molecular
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Glutamine / metabolism
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Humans
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Hydrogen-Ion Concentration
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Immunohistochemistry
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Membrane Proteins / genetics
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Membrane Proteins / metabolism*
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Membrane Transport Proteins*
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Molecular Sequence Data
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Neurotransmitter Agents / genetics
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Neurotransmitter Agents / metabolism*
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Nitrogen / metabolism*
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Organ Specificity
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Rats
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Sequence Alignment
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Sodium / metabolism
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Synapses / metabolism
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Synaptic Transmission / physiology*
Substances
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Amino Acid Transport Systems, Neutral
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Carrier Proteins
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Membrane Proteins
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Membrane Transport Proteins
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Neurotransmitter Agents
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system N protein 1
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Glutamine
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Sodium
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Nitrogen