Asparagine metabolism in mouse sarcoma cells I. Transport, metabolism and pools of dicarboxylic amino acids and their amides

Abstract

In order to grow in vitro, mouse Sarcoma-180 (S-180) cells require glutamine (2 mM) or glutamate (10 mM). A subline (S-180/ASN) was developed that can also grow in the absence of glutamine and glutamate if supplied either with asparagine (2 mM), aspartate (30 mM) or oxaloacetate (10 mM). The purpose of this study was to elucidate the cellular and metabolic differences between S-180 and S-180/ASN cells. In both cells the transport velocity of amino acids decreased in the order: glutamine≈asparagine ⪢ glutamate≈aspartate. With the exception of aspartate, the transport proceses were saturable and led to intracellular accumulation of the free amino acids. The energy of activation for the transport of asparagine by S-180 cells, which did not metabolize it, was 9.6 kcals/mole, that for aspartate 2.6 kcals/mole. The parent cells accumulated large amounts of unaltered asparagine but incorporated very little into acid-insoluble material. In the subline the conversion of asparagine to aspartate and glutamate was rapid and was directly responsible for the ability of these cells to grow on asparagine (in the absence of glutamine). The subline also differed from S-180 cells by transporting glutamate slower but metabolizing it more rapidly. The intracellular pools of amides never exceeded 3.2 mM while the corresponding acids reached up to 26 mM in cell water.