Pyrroloquinoline quinone-dependent glucose dehydrogenase anode: d-Galacturonic acid oxidation and galactaric acid production

To replace fossil resources with biomass, a lot of conversion methods have been studied. Most of each biomass-conversion usually correspond to one specific purpose, such as to produce chemicals, fuels, or energy. However, when a production of chemicals is through one or more oxidation reactions, co-production of electricity is possible through a conversion on an enzymatic bioanode in a biofuel cell. The simultaneous production will reduce the energy required for producing chemicals. According to the coproduction concept, here we show a production of meso-galactaric acid which is considered a platform chemical. meso-Galactaric acid can be obtained from C1 aldehyde oxidation of d-galacturonic acid, which exists in large quantities as pectin in food process residue. d-Galacturonic acid oxidation catalyzed by pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-GDH) and subsequent meso-galactaric acid production was confirmed for the first time by NMR measurements. PQQ-GDH is a useful catalyst for in vitro production, especially for electrosynthesis, because it requires neither the expensive cofactor nor O2. Hence, PQQ-GDH was fixed on an electrode to fabricate the PQQ-GDH electrode. The catalytic current from d-galacturonic acid oxidation with the electrode was confirmed in the electrochemical experiments to show the simultaneous production of meso-galactaric acid and the electric current.