Cloning and expression of a human neutral amino acid transporter with structural similarity to the glutamate transporter gene family

A cDNA was isolated from human brain that encodes an amino acid sequence 34-39% identical to previously published glutamate transporter sequences. Injection of RNA transcribed from this cDNA into Xenopus oocytes resulted in expression of a transport activity with the properties of the neutral amino acid uptake system ASC. Superfusion of alanine, serine, and cysteine evoked sodium-dependent inward currents in voltage-clamped oocytes expressing the transporter. These currents were dose-dependent, stereospecific, and saturable, with Km values ranging from 29 to 88 microM. Northern blot analyses revealed ubiquitous expression of this gene, termed ASCT1, consistent with the general metabolic role ascribed to system ASC.