Polyol Dehydrogenases in the Soluble Fraction of Acetobacter melanogenum

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Polyol dehydrogenases of Acetobacter melanogenum were investigated. Three polyol dehydrogenases, i. e. NAD⁺-linked D-mannitol dehydrogenase, NAD⁺-linked sorbitol dehydrogenase and NADP⁺-linked D-mannitol dehydrogenase, in the soluble fraction of the organism were purified 12-fold, 8-fold and 88-fold, respectively, by fractionation with ammonium sulfate and DEAE-cellulose column chromatography. NAD⁺-linked sorbitol dehydrogenase reduced 5-keto-D-fructose (5KF) to L-sorbose in the presence of NADH, whereas NADP⁺-linked D-mannitol dehydrogenase reduced the same substrate to D-fructose in the presence of NADPH. It was also shown that NAD⁺-linked D-mannitol dehydrogenase was specific for the interconversion between D-mannitol and D-fructose and that this enzyme was very unstable in alkaline conditions.