SUMMARY: At concentrations up to 1 mM, -asparagine was accumulated by X-2180 at 30 °C against a concentration gradient. Values for and were, respectively, 3.5 x 10 M and 33 nmol (mg dry wt) min. At concentrations below 0.1 mM, a convex curve was obtained on a Woolf-Hofstee plot, possibly indicating the presence of two -asparagine-binding sites. Autoradiograms of extracts of organisms that had accumulated labelled -asparagine revealed only one spot with an value identical with that of -asparagine. Four mutant strains lacking the ability to synthesize the general amino acid permease system grew and accumulated -asparagine at similar rates to the parent. The rate of accumulation of -asparagine from a 0.2 mM solution was greatest at pH 4.5, with the decrease in accumulation rate greater at values below than above 4.5. -Glutamine, -histidine, -methionine, -threonine and -tryptophan caused appreciable inhibition of the rate of -asparagine accumulation. With the exception of -methionine, the inhibition caused by these amino acids was competitive. Several other amino acids, including -asparagine and -aspartic acid, caused little or no inhibition of -asparagine accumulation.


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