Oxidation of Polyphenols by Extracellular Peroxidase in Suspension Cell Culture of Liverwort Heteroscyphus planus

Abstract

Peroxidase secretion and activity in the oxidation of polyphenols bisphenol A (BPA, 2,2-bis(4-hydroxyphenyl)propane) and lignin model compound (LMC, guaiacylglycerol-β-guaiacylether) were observed in a suspension cell culture of liverwort Heteroscyphus planus. When BPA was co-incubated in a suspension cell culture of liverwort for 5 days, it was depleted by approximately 63%. Oxidation of BPA was observed in culture filtrates of liverwort, and most of the oxidation products were insoluble higher molecular-weight compounds (30%). The oxidative degradation products of BPA and LMC were analyzed by GC-MS and were identified by comparing their retention time and MS spectra with those of the authentic compounds. BPA was degraded to 4-isopropenylphenol and p-hydroxyacetophenone. The formation of these products was examined using [²H₁₄]-BPA. The lignin model compound was degraded to guaiacol, vanillin, coniferyl alcohol and ferulic acid. Biphenyl dehydrodimer was detected in both the reaction mixtures of the suspension cell culture and the culture filtrates incubated with the LMC. The dimer was identified as 1,1′-(4,4′-dihydroxy-3,3′-dimethoxy-5,5′-biphenylene)- bis[8-(2″-methoxyphenoxy)-7,9-propanediol] by 1D and 2D NMR analysis. The activity of secreted peroxidase in the suspension cell culture (0.045 U/mL) was slightly enhanced by addition of LMC (0.059 U/mL), p-cresol (0.064 U/mL), and 2,6-dimethoxyphenol (0.082 U/mL) 7 days after the beginning of incubation.