Significance of glucose oxidase in lignin degradation

Abstract

GLUCOSE oxidase (EC 1.1.3.4) is commonly found in the stagnant substratum of lignocellulose degrading fungi accompanying phenol oxidases, cellulases and glucosidases1–4, where the steady-state supply of available oxygen is undoubtedly very limited5. Yet oxidants other than oxygen have heretofore received little attention as potential co-substrates of this enzyme despite its poor affinity for oxygen4,6. Spectrophotometric studies reported here on the interaction of glucose oxidase with transitory quinone and free-radical lignol oxidation products demonstrate that these intermediates are capable of serving as co-substrates of the reduced flavoenzyme at low oxygen tensions. Evidence is presented which suggests that glucose oxidase operates in concert with laccase, the principal phenol oxidase of Polyporous versicolor3,7, a typical ‘white-rot’ fungus noted for its capacity to degrade lignin1,8–12, to maintain a laccase–glucose: quinone oxidoreductase cycle in the fungal substratum by which lignol substrates may become highly oxygenated and ultimately degraded.