PATHWAYS FOR METABOLISM OF KETOALDONIC ACIDS IN AN ERWINIA SP

The pathways involved in the metabolism of ketoaldonic acids by Erwinia sp. strain ATCC 39140 have been investigated by use of a combination of enzyme assays and isolation of bacterial mutants. The catabolism of 2,5-diketo-D-gluconate (2,5-DKG) to gluconate can proceed by two separate NAD(P)H-dependent pathways. The first pathway involves the direct reduction of 2,5-DKG to 5-keto-D-gluconate, which is then reduced to gluconate. The second pathway involves the consecutive reduction of 2,5-DKG to 2-keto-L-gulonate and L-idonic acid, which is then oxidized to 5-keto-D-gluconate, which is then reduced gluconate. Gluconate, which can also be produced by the NAD(P)H-dependent reduction of 2-keto-D-gluconate, is phosphorylated to 6-phosphogluconate and further metabolized through the pentose phosphate pathway. No evidence was found for the existence of the Entner-Doudoroff pathway in this strain.