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 glucosidases^1–4, 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 oxygen^4,6. 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 versicolor^3,7, a typical ‘white-rot’ fungus noted for its capacity to degrade lignin^1,8–12, to maintain a laccase–glucose: quinone oxidoreductase cycle in the fungal substratum by which lignol substrates may become highly oxygenated and ultimately degraded.