Formation of arabinose, ribulose and tartronic acid from 2-keto-D-gluconic acid.

For some years evidence that 2-keto-D-gluconic acid is implicated in a number of biochemical systems, notably in Acetobacter species (Bernhauer & Gorlich, 1935; Kulka & Walker, 1954) and in Pseudomonas species (Lockwood, Tabenkin & Ward, 1941; Norris & Campbell, 1949) has been accumulating. Studies by Warburg & Christian (1937) with red blood cells, by Lipmann (1936) with yeast macerate preparations and by Dickens (1938) with crude enzyme preparations from yeast, afforded substantial evidence for the existence of a pathway for the direct oxidation of glucose 6-phosphate by way of 6-phosphogluconie acid, 2-keto-6-phosphogluconic acid and pentose 5-phosphate. The work of Cohen & Scott (1951) with yeast preparations confirmed this scheme, since they detected the presence of 2-keto-6-phosphogluconate, ribose 5-phosphate and glyceraldehyde 3-phosphate in experiments on the oxidation of 6-phosphogluconate. We have recently isolated 2-keto-D-gluconic acid and tartronic acid from a culture of Acetobacter acetosum on a glucose medium (Kulka, Hall & Walker, 1951). Tartronic acid had not been identified previously as a product of bacterial metabolism, although its presence in sugar-refinery liquor had been established by von Lippmann (1913). According to Rieben & Hastings (1946), tartronic acid is formed in various plants. In view of the isolation of this acid from bacterial cultures under conditions which might suggest that it was a decomposition product of 2-keto-D-gluconic acid, we have studied the decomposition of the latter under similar conditions. Our experiments have shown that tartronic acid was definitely formed and probably arabinose and ribulose.