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Accumulation of L-Asparagine by Saccharomyces cerevisiae X-2180
Abstract
At concentrations up to 1 mm, l-asparagine was accumulated by Saccharomyces cerevisiae X-2180 at 30 °C against a concentration gradient. Values for K T and V max were, respectively, 3.·5 × 10−4 M and 33 nmol (mg dry wt)−1 min−1. At concentrations below 0·1 mm, a convex curve was obtained on a Woolf-Hofstee plot, possibly indicating the presence of two l-asparagine-binding sites. Autoradiograms of extracts of organisms that had accumulated labelled l-asparagine revealed only one spot with an R F value identical with that of l-asparagine. Four mutant strains lacking the ability to synthesize the general amino acid permease system grew and accumulated l-asparagine at similar rates to the parent. The rate of accumulation of l-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. l-Glutamine, l-histidine, l-methionine, l-threonine and l-tryptophan caused appreciable inhibition of the rate of l-asparagine accumulation. With the exception of l-methionine, the inhibition caused by these amino acids was competitive. Several other amino acids, including d-asparagine and l-aspartic acid, caused little or no inhibition of l-asparagine accumulation.
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© Society for General Microbiology 1982