Electrochemical H2O2 - stat mode as reaction concept to improve the process performance of an unspecific peroxygenase.

The electroenzymatic hydroxylation of 4-ethylbenzoic acid catalyzed by the recombinant unspecific peroxygenase from the fungus Agrocybe aegerita (r Aae UPO) was performed in a gas diffusion electrode (GDE)-based system. Enzyme stability and productivity are significantly affected by the way the co-substrate hydrogen peroxide (H 2 O 2) is supplied. In this study, two in-situ electrogeneration modes of H 2 O 2 were established and compared. Experiments under galvanostatic conditions (constant productivity of H 2 O 2) were conducted at current densities spanning from 0.8 mA cm−2 to 6.4 mA cm−2. For comparison, experiments under H 2 O 2 -stat mode (constant H 2 O 2 concentration) were performed. Here, four H 2 O 2 concentrations between 0.06 mM and 0.28 mM were tested. A maximum H 2 O 2 productivity of 5.5 µM min−1 cm−2 and productivity of 10.5 g L−1 d−1 were achieved under the galvanostatic condition at 6.4 mA cm−2. Meanwhile, the highest total turnover number (TTN) of 710,000 mol mol−1 and turnover frequency (TOF) of 87.5 s−1 were obtained under the H 2 O 2 -stat mode at concentration limits of 0.15 mM and 0.28 mM, respectively. The most favorable outcome in terms of maximum achievable TTN, TOF and productivity was found under the H 2 O 2 -stat mode at concentration limit of 0.2 mM. Here, a TTN of 655,000 mol mol−1, a TOF of 80.3 s−1 and a productivity of 6.1 g L−1 d−1 were achieved. The electrochemical H 2 O 2 -stat mode not only offers a promising alternative reaction concept to the well-established galvanostatic mode but also enhances the process performance of unspecific peroxygenases. [Display omitted] • In-situ electrochemical H 2 O 2 -stat mode as a promising alternative reaction concept. • Combination of electrochemical H 2 O 2 -stat mode with an enzymatic hydroxylation. • Enhancement of process performance of unspecific peroxygenase. • Achievement of TTN up to 710,000 mol mol−1 and TOF as high as 87.5 s−1 [ABSTRACT FROM AUTHOR]