Abstract
The mitochondrial carriers are a family of transport proteins that, with a few exceptions, are found in the inner membranes of mitochondria. They shuttle metabolites and cofactors through this membrane, and connect cytoplasmic functions with others in the matrix. SAM (S-adenosylmethionine) has to be transported into the mitochondria where it is converted into S-adenosylhomocysteine in methylation reactions of DNA, RNA and proteins. The transport of SAM has been investigated in rat liver mitochondria, but no protein has ever been associated with this activity. By using information derived from the phylogenetically distant yeast mitochondrial carrier for SAM and from related human expressed sequence tags, a human cDNA sequence was completed. This sequence was overexpressed in bacteria, and its product was purified, reconstituted into phospholipid vesicles and identified from its transport properties as the human mitochondrial SAM carrier (SAMC). Unlike the yeast orthologue, SAMC catalysed virtually only countertransport, exhibited a higher transport affinity for SAM and was strongly inhibited by tannic acid and Bromocresol Purple. SAMC was found to be expressed in all human tissues examined and was localized to the mitochondria. The physiological role of SAMC is probably to exchange cytosolic SAM for mitochondrial S-adenosylhomocysteine. This is the first report describing the identification and characterization of the human SAMC and its gene.
Publication types
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Comparative Study
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Research Support, Non-U.S. Gov't
MeSH terms
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Amino Acid Sequence
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Amino Acid Transport Systems
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Animals
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Biological Transport / drug effects
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Brain Chemistry
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Bromcresol Purple / pharmacology
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CHO Cells
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Calcium-Binding Proteins / antagonists & inhibitors
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Calcium-Binding Proteins / genetics*
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Calcium-Binding Proteins / isolation & purification
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Calcium-Binding Proteins / physiology
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Cloning, Molecular
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Cricetinae
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Cytosol / metabolism
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DNA, Complementary / genetics
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Escherichia coli
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Expressed Sequence Tags
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Genes*
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Humans
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Hydrolyzable Tannins / pharmacology
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Membrane Transport Modulators
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Membrane Transport Proteins / antagonists & inhibitors
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Membrane Transport Proteins / genetics*
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Membrane Transport Proteins / isolation & purification
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Membrane Transport Proteins / physiology
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Mitochondria / metabolism*
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Mitochondrial Proteins / antagonists & inhibitors
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Mitochondrial Proteins / genetics*
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Mitochondrial Proteins / isolation & purification
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Mitochondrial Proteins / physiology
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Molecular Sequence Data
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Nerve Tissue Proteins / genetics
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Nerve Tissue Proteins / isolation & purification
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Organ Specificity
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Phylogeny
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RNA, Messenger / biosynthesis
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Recombinant Fusion Proteins / metabolism
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S-Adenosylhomocysteine / metabolism*
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S-Adenosylmethionine / metabolism*
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Sequence Alignment
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Sequence Homology, Amino Acid
Substances
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Amino Acid Transport Systems
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Calcium-Binding Proteins
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DNA, Complementary
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Hydrolyzable Tannins
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Membrane Transport Modulators
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Membrane Transport Proteins
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Mitochondrial Proteins
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Nerve Tissue Proteins
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RNA, Messenger
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Recombinant Fusion Proteins
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SLC25A26 protein, human
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Bromcresol Purple
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S-Adenosylmethionine
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S-Adenosylhomocysteine