Cation-independent electroneutral transporter (not associated with membrane depolarization) of a variety of tricarboxylic and dicarboxylic acid-cycle intermediates. There is also small, but detectable, transport of monocarboxylics. Transport is through the epithelium of the gut and across the plasma membranes of organs involved in intermediary metabolism and storage. Affinity for substrates is citrate > succinate > pyruvate. Fumarate, a-ketoglutarate, and glutarate are also transported, but not lactate. Transport mechanism that is not coupled to Na(+), K(+), or Cl(-). Function is shown in Xenopus oocytes and human retinal pigment epithelial (HRPE) cell lines. Basolateral membrane of cells in the midgut. In adults, abundantly expressed in the fat body, basolateral region of midgut cells and oenocytes. Low level expression is seen in the halteres, procardia, restricted regions of the esophagus and hindgut, base of the legs and in a subset of cells in the third segment of the antennae. Completely inhibited by DIDS. Modest but significant inhibition by phloretin or furosemide. The life-extending effect of mutations is likely caused by an alteration in energy balance caused by a decrease in transport function. Belongs to the SLC13A/DASS transporter (TC 2.A.47) family. NADC subfamily.