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In order to improve the stability of oxalate decarboxylase (Oxdc), response surface methodology (RSM), based on a four-factor three-level Box-Behnken central composite design was used to optimize the reaction conditions of oxalate decarboxylase (Oxdc) modified with monomethoxy polyethyleneglycol (mPEG5000). Four independent variables such as the ratio of mPEG-aldehyde to Oxdc, reaction time, temperature, and reaction pH were investigated in this work. The structure of modified Oxdc was identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Fourier transform infrared (FTIR) spectroscopy, the stability of the modified Oxdc was also investigated. The optimal conditions were as follows: the mole ratio of mPEG-aldehyde to Oxdc of 1:47.6, time of 13.1 h, temperature at 29.9 °C, and the reaction pH of 5.3. Under optimal conditions, experimental modified rate (MR = 73.69%) and recovery rate (RR = 67.58%) were matched well with the predicted value (MR = 75.11%) and (RR = 69.17%). SDS-PAGE and FTIR analysis showed that mPEG was covalently bound to the Oxdc. Compared with native Oxdc, the modified Oxdc (mPEG-Oxdc) showed higher thermal stability and better tolerance to trypsin or different pH treatment. This work will provide a further theoretical reference for enzyme modification and conditional optimization.

In this article, a graphite felt electrode was modified by NS double‐element and NB double‐element codoping. The surface morphology, crystal structure, element content, and surface chemical state of the modified electrode were characterized by scanning electron microscopy, X‐ray powder diffraction (XRD), Raman spectroscopy, and X‐ray photoelectron spectroscopy. The electrochemical performance of the modified electrode was evaluated by cyclic voltammetry, electrochemical impedance spectra, and a single cell. The results show that nitrogen (N) and boron (B) double‐element codoping can enhance the catalytic activity of graphite felt and create abundant defect sites, which increases the electrocatalytic activity by approximately a factor of 2. The reason why the doped graphite felt can obtain higher electrocatalytic activity may be related to the synergy between N and B atoms, especially the synergy between pyridine‐N and BC3, and the resistance of the first charge transfer reaction of 1,8‐dihydroxyanthraquinone on the doped graphite felt electrode is then reduced.