Transport of <scp>l</scp>‐Aspartate and <scp>l</scp>‐Glutamate in Plasma‐Membrane Vesicles from Rat Liver

Abstract

An Na + concentration gradient (outside &gt; inside) drives the uphill transport of l ‐aspartate and l ‐glutamate in rat‐liver plasma membrane vesicles. Competition and exchange‐diffusion experiments indicate the presence of a transport system specific for l ‐aspartate and l ‐glutamate with a high substrate affinity: an apparent K m of 5.4 μM and 7.4 μM was found for l ‐aspartate and l ‐glutamate, respectively. The uphill transport is Na + ‐specific, but also requires the presence of K + for optimal functioning. The possible physiological relevance of such a transport system is discussed.