MNF3841 grown on glucose/NHCl constitutively transported L-asparagine, L-aspartate, L-glutamate, L-glutamine, glycine, L-leucine, L-methionine and L-phenylalanine. Transport rates were increased 1.5-4-fold by growth on glucose/L-glutamate. Uptake of L-glutamate, L-glutamine, L-asparagine and L-leucine was inhibited to varying extents by a broad range of L-amino acids. Analogues of L-glutamate in which the amino group or α;-hydrogen was methylated inhibited L-glutamate transport much less effectively. Also while 2-and 3-amino acids interfered with L-glutamate uptake, D-glutamate did not. Inhibition by 2,4-dinitrophenol, carbonyl cyanide -chlorophenylhydrazone and cyanide indicated that amino acid transport was active. The ratio of the intracellular to extracellular concentration of L-leucine after 5 min accumulation was 768. Cells loaded with L-[C]leucine exhibited exchange not only with external L-leucine but also with L-glutamate. The apparent for L-glutamate transport was 0.081 μ;m. Both L-aspartate and L-alanine were competitive inhibitors of L-glutamate uptake with apparent values of 0.164 μ;m and 2.3 μ;m, respectively. These results suggest that there is an extremely high affinity carrier for L-glutamate that is not only very sensitive to inhibition by L-aspartate but also capable of being inhibited by a broad range of amino acids at an order of magnitude higher concentration.


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