Proteus mirabilis dehydrogenates aldonates and aldarates with an (R)-configured alpha-carbon atom to the corresponding 2-oxocarboxylates.

Resting cells of Proteus mirabilis effectively dehydrogenate aldonates and aldarates to the corresponding 2-oxocarboxylates (Figure 2). The prerequisite is an (R)-configured alpha-carbon atom next to the carboxylate group. The oxidation reagent is dimethylsulfoxide and the electron mediator is anthraquinone-2,6-disulfonate (Figure 1). The reactions mostly proceed quantitatively in concentrations up to 0.5 M. The two enzymes necessary for the dehydrogenation, (2R)-hydroxycarboxylate viologen oxidoreductase and dimethylsulfoxide reductase, are present in P. mirabilis in high activities. Nine aldonates have been dehydrogenated to 2-glyculosonates (2-oxoaldonates) and two aldarates to alpha-oxo aldarates. As shown with lactobionate and 6-phospho-D-gluconate, derivatives of aldonates can be dehydrogenated too. The apparent Km values of the substrates are often < 1 mM. The products were isolated as sodium or potassium salts with yields between 65 and 98% and characterized. D-xylo-Hex-2-ulosonate obtained from D-gulonate was converted to D-ascorbic acid.