Oxidative degradation of phenolic compounds by versatile peroxidase-mediated Mn(III) complex system

Abstract:

[Background] Phenolic compounds are among the main water pollutants in the environment. The Mn(III) -organic acid chelate mediated by versatile peroxidase (VP) is considered to have great potential in the degradation of phenolic organic pollutants owing to the high redox potential. [Objective] To explore the degradation of phenolic compounds by VP-mediated Mn(III)-organic acid chelate and thereby to provide a new mindset and method for the biodegradation of phenolic compounds. [Methods] The active VP from Pleurotus eryngii (PeVP) was obtained by renaturation of inclusion body in vitro. We characterized the enzymatic properties of PeVP and optimized the reaction conditions of Mn(III) chelate to explore the ability of the complex system to degrade the phenolic compounds. [Results] The optimum conditions for renaturation of PeVP were as follows:The inclusion body was refolded in pH 9.5 solution containing 0.5 mol/L urea, 0.5 mmol/L oxidized glutathione (GSSG), 0.1 mmol/L dithiothreitol (DTT), 0.1 mmol/L ethylenediamine tetraacetic acid (EDTA), 5 mmol/L CaCl₂, 10% glycerol, and 5 µmmol/L hematin at 4℃ for 24 h, and then incubated with 5 µmol/L hematin for 12 h. The optimal reaction conditions of PeVP-mediated Mn(III)-organic acid chelate were 75 mmol/L malic acid buffer (pH 4.5), 6 mmol/L Mn²⁺, and 0.2 mmol/L H₂O₂. Under the above conditions, the catalytic activity of the chelate system on phenolic compounds 2,2ʹ-azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS), 2,6-dimethoxyphenol (DMP), guaiacol, and syringaldazine was detected, and it was found that the oxidation activity of Mn(III) chelate system at pH 4.5 was 1.5-7.5 times that of PeVP alone. Moreover, the average degradation rates of phenol, hydroquinone, resorcinol, and p-nitrophenol by Mn(III)-malic acid chelate system were 10.91, 10.69, 6.50, 5.71 mg/(L·h), respectively. Therefore, the Mn(III)-organic acid complex might capture the electrons of phenolic substrate to form phenolic free radicals and lead to the fracture of benzene ring with the decrease of bond energy, thus achieving the oxidative degradation of phenolic compounds. [Conclusion] At pH 4.5, Mn(III)-malic acid chelate system mediated by PeVP shows strong ability to oxidize phenolic substrates, which is a promising solution for the biodegradation of phenolic organic pollutants.

Key words:versatile peroxidase;inclusion body renaturation;Mn(III)-malic acid chelate;phenolic pollutants;oxidative degradation