A biosynthesis of dimethylpyruvic acid

1. 1. Out of nine strains of Aspergillus niger which were tested, eight proved capable of forming pyruvic and dimethylpyruvic acids when their pre-formed mycelial felts were allowed to act upon glucose in the presence of NH 4Cl, KH 2PO 4, and Na 2SO 3, in the proportions recommended by Hida ( loc. cit.). When NH 4Cl was omitted from the medium the yield of pyruvic acid was undiminished, but that of dimethylpyruvic acid fell to a negligible amount. 2. 2. In Hida's medium both pyruvic and dimethylpyruvic acids were also formed by A. niger when d-xylose and glycerol, respectively, were used in place of glucose as substrate. 3. 3. In one experiment, addition of sodium malonate to the medium when glycerol was the substrate caused a slight increase in the yield both of pyruvic acid and of dimethylpyruvic acid, but in each case this increase was so small as to render its significance doubtful. Addition of sodium acetate to the glycerol medium caused a very large increase in the yield of pyruvic acid and a substantial increase also in the yield of dimethylpyruvic acid, when the molecular ratio of glycerol to acetate lay between 3:1 and 2:1. When acetate was added in excess of the molecular ratio 1:1, neither pyruvic acid nor dimethylpyruvic acid was formed. 4. 4. Tentative suggestions are advanced respecting the mechanisms by which dimethylpyruvic acid may be derived from glycerol.