Hydrogen Peroxide-Producing Enzymes

Fungi, white-rot basidiomycetes in particular, require H2O2 to allow the extra­cellular peroxidase enzymes to function in lignin degradation. The H2O2 is pro­vided by oxidases that are produced by the fungus and act by reducing molecular O2 to H2O2 alongside the oxidation of a co-substrate (Dashtban et al. 2009; Isroi et al. 2011). Two such oxidases are glyoxal oxidase (GLOX; EC 1.2.3.5) and aryl alcohol oxidase (AAO; EC 1.1.3.7). GLOX is a copper-containing enzyme found in many white-rot fungi, for example P. chrysosporium, and can oxidise a variety of co-substrates, typically simple aldehydes (Isroi et al. 2011; Martrnez et al. 2005). Some of these substrates are natural substances produced by the metabolism of the fungus, for example, glyoxal and methylglyoxal (Isroi et al. 2011). AAO, a flavoenzyme first discovered in P. eryngii, acts upon specific metabolites of the white-rot fungi to give rise to H2O2. Chlorinated anisyl alcohols are among the substrates oxidised by this enzyme as well as aromatic aldehydes released during lignin degradation in the presence of aryl alcohol dehydrogenase (AAD; EC 1.1.1.91) (Isroi et al. 2011; Martrnez et al. 2005).

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