BIOASSAY OF LIPOIC ACID WITH STREPTOCOCCUS FAECALIS 10 C1

Abstract

A tube assay procedure for lipoic acid with Streptococcus faecalis 10 C1 was presented. The growth of the organism in a synthetic medium containing 0.125% of sodium propionate and various amounts of lipoic acid at 37℃ for 15-20 hours was measured turbidimetrically with an electrophotometer. A sufficient growth response was obtained to 0-0.25 mγ of L-lipoic acid per cc of the assay medium. An acid hydrolysis in 6N H_2SO_4 at 120℃ for 1 hour was carried out in order to liberate lipoic acid from natural substances. Discussion was made on the stability of lipoic acid in the acid treatment and the effect of sodium sulfate formed by neutralizing the extract with sodium hydroxide and, furthermore, on several problems in the application of this procedure to urine. The existence of an unknown substance in the mycelium of Aspergillus oryzae which stimulates the growth of the test organism under the same condition as this assay method was also cited.