Identification of malic acid from yeast.

Evidence indicated an accumulation of l-malic acid in the synthetic growth medium of both lysine auxotrophs and wild-type yeast. Malic acid was isolated from growth experiments and was identified by paper and column chromatography, by comparison of infrared spectra with authentic l-malic acid, as well as enzymatically, as a substrate of malic dehydrogenase. Malic acid was accumulated when glucose was used as a carbon source. This did not occur when sodium lactate was the carbon source. Malic, succinic, and citric acids, and a few other as yet unidentified organic acids, were accumulated in the culture supernatant fluid when yeast was grown in a chemically defined medium. The accumulation of these acids had no obvious relation to the pathway for lysine biosynthesis.