SODIUM-DEPENDENT HOMO-EXCHANGE AND HETERO-EXCHANGE OF NEUTRAL AMINO-ACIDS MEDIATED BY THE AMINO-ACID TRANSPORTER ATB-DEGREES

We have investigated the functional characteristics of the human amino acid transporter ATB degrees using the Xenopus laevis oocyte expressi on system. When expressed in oocytes, ATB degrees mediates the uptake of neutral amino acids in an Na+-dependent manner. In addition, this t ransporter is able to mediate the efflux of intracellular neutral amin o acids in exchange with extracellular neutral amino acids. This homo- and hetero-exchange of amino acids is absolutely Na+-dependent and co nforms strictly to the substrate specificity of ATB degrees. Kinetic a nalysis indicates that the affinity of ATB degrees for a given amino a cid substrate is similar whether ATB degrees catalyzes the influx of t he amino acid or the amino acid-induced efflux of intracellular amino acids. These results demonstrate for the first time the ability of ATB degrees to function as a homo- and hetero-exchanger for its substrate s. (C) 1998 Academic Press.