Integration of Formate Dehydrogenase and Glycerol Dehydrogenase with Electrochemical NADH Regeneration for Enhanced Waste Valorization

Abstract

This study evaluates the effects of coupling the system by immobilizing formate dehydrogenase (FDH) and glycerol dehydrogenase (GlyDH) enzymes, individually and co-immobilized, on mesoporous silica with the electrochemical NADH regeneration. In the enzyme immobilization process three protein loadings were studied, and the biocatalysts obtained were characterized in terms of immobilization yield in protein, retained activity and thermal stability. Temperature and pH profiles were determined, as well. The FDH/GlyDH multienzymatic system was studied with and without electrochemical cofactor regeneration. The effect of the enzyme activity ratio (UFDH:UGlyDH), aiming to maximize formic acid and DHA production, was studied in the absence of electrochemical cofactor regeneration. The UFDH:UGlyDH ratio of 1:8 resulted to be the most favorable condition, showing a production of 2.5 mM of formic acid and 17 mM for dihydroxyacetone (DHA).

The successful regeneration of the NADH cofactor during CO2 reduction, for both approaches, with and without the electrochemical method, was confirmed by the increase of formic acid concentration. Notably, similar formic acid production outcomes were observed across all regeneration systems. Co-immobilization of the enzyme resulted in faster formic acid production in the early stages of the reaction, but then slows down and approaches the case of individually immobilized enzymes, suggesting that the reverse reaction takes place.

Keywords: Enzyme immobilization, amino silica, CO2 conversion, NADH regeneration, bioelectrochemistry