SYNTHESIS OF ASPARTIC ACID BY LACTOBACILLUS ARABINOSUS

Abstract

Lactobacillus arabinosus was grown on a complex synthetic medium and the synthesis of aspartic acid studied using the tracer compounds carbon dioxide-C¹⁴, glucose-6-C¹⁴, glucose-2-C¹⁴, or ammonium chloride-N¹⁵. The β-carboxyl carbon of aspartic acid was derived to a major extent or solely from carbon dioxide-C¹⁴and no radioactivity was found in the α-carboxyl. Approximately half of the β-carbon atoms of aspartic acid were derived from carbon 6 of glucose and half of the α-carbon atoms from carbon 2 of glucose. The amino group of aspartic acid was derived to only a minor extent from ammonium chloride-N¹⁵and the isotope concentration was the same as that found in glutamic acid. The results indicate that aspartic acid is formed by the carboxylation of two three-carbon fragments derived from glucose, followed by transamination.Malic acid or oxalacetic acid added to the medium was not used to a significant extent in the synthesis of aspartic acid. The addition of aspartic acid to the medium caused a net decrease in the amount of aspartic acid synthesized, and the effect was more marked in low-biotin medium.