Probing Reactivity of PQQ-Dependent Carbohydrate Dehydrogenases Using Artificial Electron Acceptor

The kinetic parameters of carbohydrate oxidation catalyzed by Acinetobacter calcoaceticus pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase (GDH) and Escherichia coli PQQ-dependent aldose sugar dehydrogenase (ASDH) were determined using various electron acceptors. The radical cations of organic compounds and 2,6-dichlorophenolindophenol are the most reactive with both enzymes in presence of glucose. The reactivity of dioxygen with ASDH is low; the bimolecular constant k _ox = 660 M⁻¹ s⁻¹, while GDH reactivity with dioxygen is even less. The radical cation of 3-(10H-phenoxazin-10-yl)propionic acid was used as electron acceptor for reduced enzyme in the study of dehydrogenases carbohydrates specificity. Mono- and disaccharide reactivity with GDH is higher than the reactivity of oligosaccharides. For ASDH, the reactivity increased with the carbohydrate monomer number increase. The specificity of quinoproteins was compared with specificity of flavoprotein Microdochium nivale carbohydrate oxidase due to potential enzymes application for lactose oxidation.