PMID: 7372663May 10, 1980Paper

Characteristics of an amino acid transport system in rat liver for glutamine, asparagine, histidine, and closely related analogs.

The Journal of Biological Chemistry
M S KilbergH N Christensen

Abstract

In the rat hepatocyte, whether freshly separated or in primary culture, we do not find L-glutamine entry by Systems A and ASC as seen in cells previously studied. Instead the mediated entry of glutamine appears to occur exclusively by a Na+-dependent system ("N") apparently specific to amino acid amides and L-histidine; however, a portion of asparagine uptake occurs by System A. The simplest evidence for the separateness of the added system is the failure of model substrates for System A (e.g. N-methylalanine) to inhibit glutamine uptake significantly, and the failure of glutamine to inhibit the uptake of L-cysteine, model substrate for System ASC, at least in this cell. As is the case for cysteine, glutamine inhibits transport by System A (although not competitively), even though showing no transport by that system. Our finding confirms an earlier inference that glutamine uptake by this cell may follow a route not taken by alanine or serine, and explains the apparently erroneous companion inference that glutamine also shares a route with these two amino acids. Its uptake has now been characterized to show a series of differences from Systems A and ASC. Especially significant in view of the importance of glutamine metabolism ar...Continue Reading

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