L-2-Keto-4,5-dihydroxyvaleric acid: an intermediate in the oxidation of L-arabinose by Pseudomonas saccharophila.

Crude cell-free preparations of Pseudomonas saccharophila grown on n-arabinose oxidize n-arabinose to ol-ketoglutaric acid (1). n-Arabonic acid has been identified as an intermediate in this reaction. The investigations described in this communication are concerned with the mechanism of the conversion of Larabonate to a-ketoglutarate. Evidence is presented for the intermediate formation of &2-keto-4,5-dihydroxyvaleric acid, a 2-keto-3-deoxy sugar acid, in the transformation. In this respect the metabolism of n-arabinose is similar to that of the n-isomer which is dehydrated to n-2-keto-4,5-dihydroxyvaleric acid (2). The metabolism of Dand Irarabinose differs in that the n-form of the keto acid intermediate is oxidatively cleaved to pyruvic and glycolic acids while the bisomer is converted to cy-ketoglutaric acid. The over-all reaction sequence, as it is now known, in the metabolism of n-arabinose by P. saccharophila can be represented as follows: