Oxidation of isomaltose, gentiobiose, and melibiose by membrane-bound quinoprotein glucose dehydrogenase from acetic acid bacteria

Membrane-bound quinoprotein glucose dehydrogenase from acetic acid bacteria produces lactobionic acid by the oxidation of lactose. Its enzymatic activity on lactose and maltose is much lower than that on D-glucose. For that reason, the activity of the enzyme on disaccharides has been considered low. In this study, we show that the isomaltose-oxidizing activity of acetic acid bacteria is much higher than their lactose-oxidizing activity. In addition to isomaltose, the enzyme oxidized gentiobiose and melibiose to the same extent. According to the characteristics of the isomaltose-oxidizing activity and investigations using dehydrogenase-deficient mutant bacteria, we identified the responsible enzyme as membrane-bound quinoprotein glucose dehydrogenase. Abbreviations: AAB: acetic acid bacteria; m-GDH: membrane-bound quinoprotein glucose dehydrogenase; DCIP: 2,6-dichlorophenolindophenol; DP: degree of polymerization; HPAEC-PAD: high-performance anion-exchange chromatography with pulsed amperometric detection; NMR: nuclear magnetic resonance; TLC: thin layer chromatography; COSY: correlation spectroscopy Membrane-bound quinoprotein glucose dehydrogenase (m-GDH) from acetic acid bacteria oxidizes disaccharides having α/β-1➝6 glycosidic linkages.