title: Functional characterization of high-affinity Na(+)/dicarboxylate cotransporter found in Xenopus laevis kidney and heart.
abstract: The SLC13 gene family includes sodium-coupled transporters for citric acid cycle intermediates and sulfate. The present study describes the sequence and functional characterization of a SLC13 family member from Xenopus laevis, the high-affinity Na(+)/dicarboxylate cotransporter xNaDC-3. The cDNA sequence of xNaDC-3 codes for a protein of 602 amino acids that is approximately 70% identical to the sequences of mammalian NaDC-3 orthologs. The message for xNaDC-3 is found in the kidney, liver, intestine, and heart. The xNaDC-3 has a high affinity for substrate, including a K(m) for succinate of 4 muM, and it is inhibited by the NaDC-3 test substrates 2,3-dimethylsuccinate and adipate. The transport of succinate by xNaDC-3 is dependent on sodium, with sigmoidal activation kinetics, and lithium can partially substitute for sodium. As with other members of the family, xNaDC-3 is electrogenic and exhibits inward substrate-dependent currents in the presence of sodium. However, other electrophysiological properties of xNaDC-3 are unique and involve large leak currents, possibly mediated by anions, that are activated by binding of sodium or lithium to a single site.
authors.affiliation: Department of Human Biological Chemistry and Genetics, University of Texas Medical Branch, 301 University Blvd., Galveston, TX 77555-0645, USA.
authors.forename: Naomi
authors.initials: N
authors.lastname: Oshiro
authors.forename: Ana M
authors.initials: AM
authors.lastname: Pajor
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001693:Biological Transport, Active; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D002462:Cell Membrane / Q000502:physiology; D006321:Heart / Q000502:physiology*; D007413:Intestinal Mucosa / Q000378:metabolism; D007668:Kidney / Q000378:metabolism*; D008094:Lithium / Q000502:physiology; D008099:Liver / Q000378:metabolism; D008564:Membrane Potentials / Q000502:physiology; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D009865:Oocytes / Q000502:physiology; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012964:Sodium / Q000502:physiology; D013379:Substrate Specificity; D019802:Succinic Acid / Q000378:metabolism; D014018:Tissue Distribution; D014982:Xenopus laevis
chemical_list: D002352:Carrier Proteins; D026901:Membrane Transport Proteins; D008094:Lithium; D012964:Sodium; D019802:Succinic Acid