Transport of acidic amino acids by human jejunal brush-border membrane vesicles.
This study characterizes the transport of radiolabeled acidic amino acids into brush-border membrane vesicles prepared from human jejunum. The uptakes of L-glutamic, L-aspartic, and D-aspartic acids were stimulated by a Na+ gradient (extravesicular greater than intravesicular). Concentrative uptake (resulting in an "overshoot" phenomenon) of these dicarboxylic amino acids occurred when there was an outward K+ gradient (intravesicular greater than extravesicular). In addition, increasing K+ gradients (0-100 mM) resulted in enhanced uptake of L-glutamic acid. This K+ requirement is somewhat specific as Rb+ and Cs+ could enhance uptake to a limited extent, whereas Li+ and choline+ showed no enhancement. The presence of a K+ gradient did not affect the affinity of the carrier system for L-glutamic acid but it did increase the Vmax. The presence of extravesicular anions having differing membrane permeabilities did not alter L-glutamic acid uptake indicating an absence of an effect of membrane potential on the transport process. Finally, the human transport system for L-glutamic acid appears to be specific for acidic amino acids as demonstrated by inhibition studies. Our studies demonstrate a transport system in human jejunum specific for acidic amino acids that is energized by an inward Na+ gradient and an outward K+ gradient.
D001224:Aspartic Acid / Q000378:metabolism*; D001692:Biological Transport; D005971:Glutamates / Q000378:metabolism*; D018698:Glutamic Acid; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D007583:Jejunum / Q000378:metabolism*; D007700:Kinetics; D007930:Leucine / Q000378:metabolism; D008239:Lysine / Q000378:metabolism; D008871:Microvilli / Q000378:metabolism*; D013237:Stereoisomerism
D005971:Glutamates; D001224:Aspartic Acid; D018698:Glutamic Acid; D007930:Leucine; D008239:Lysine