Single electron reduction of xenobiotic compounds by glucose oxidase from Aspergillus niger

Various species of fungi express glucose oxidase that catalyzes formation of gluconolactone from glucose with concomitant, direct divalent reduction of molecular oxygen to hydrogen peroxide. A physiological function ascribed to this extracellular enzyme is production of hydrogen peroxide for use in lignin degradation catalyzed by lignin peroxidases. Herein, we show that glucose oxidase can catalyze one-electron reduction of several different classes of xenobiotic compounds resulting in generation of free radical products. Electron spin resonance (ESR) spectroscopy was used to visualize the one-electron reduction products of 4-nitropyridine-N-oxide (4NPO), 1,4-naphthoquinone (1,4NQ), and dichlorophenolindolphenol (DCPIP). Hyperfine splitting constants were used to generate computer simulations of the spectra confirming the presence of free radical products.