Hexuronic Acid Dehydrogenase of Agrobacterium tumefaciens

Growth ofAgrobacterium tumefaciens ond -glucuronic acid (GlcUA) ord -galacturonic acid (GalUA) induces formation of hexuronic acid dehydrogenase [d -aldohexuronic acid: nicotinamide adenine dinucleotide (NAD) oxidoreductase]. The dehydrogenase, which irreversibly converts GlcUA or GalUA to the corresponding hexaric acid with the concomitant reduction of NAD, but not of nicotinamide adenine dinucleotide phosphate was purified 60-fold by MnCl2 treatment, (NH4 )2 SO4 fractionation, chromatography on diethylaminoethyl Sephadex and negative adsorption with Ca3 (PO4 )2 gel. Thep H optimum is 8.0. Other uronic acids, aldohexoses, aldopentoses, and polyols, are not substrates. Reduced nicotinamide adenine dinucleotide is an inhibitor strictly competitive with NAD. Kinetic data indicate that the dehydrogenase induced by growth on GlcUA may not be identical with that induced by growth on GalUA.