Catabolism of d -Glucaric Acid to α-Ketoglutarate in Bacillus megaterium

Crude cell-free extracts of d-glucarate-grown cells of Bacillus megaterium converted d-glucarate to alpha-keto-beta-deoxy-d-glucarate (KDG). Charcoal-treated cell-free extracts or partially purified enzyme preparations converted KDG to an intermediate which was isolated and identified as 2,5-diketoadipate (DKA). This compound was synthesized, and the cell-free extracts of d-glucarate grown cells were found to catalyze the reduction of nicotinamide adenine dinucleotide (NAD) in its presence. In the absence of NAD, the same enzyme preparation catalyzed the decarboxylation of the DKA to alpha-ketoglutarate semialdehyde (KGS), whereas in the presence of NAD the KGS was subsequently oxidized to alpha-ketoglutarate by alpha-ketoglutarate semialdehyde dehydrogenase. Since galactarate-grown B. megaterium contains a galactarate dehydrase forming KDG, the complete pathway for the metabolism of d-glucarate or galactarate to alpha-ketoglutarate and CO(2) is now known in a gram-positive bacterium.