Lignin-degrading enzyme from Phanerochaete chrysosporium : Purification, characterization, and catalytic properties of a unique H 2 O 2 -requiring oxygenase

Abstract

An extracellular lignin-degrading enzyme from the basidiomycete Phanerochaete chrysosporium Burdsall was purified to homogeneity by ion-exchange chromatography. The 42,000-dalton ligninase contains one protoheme IX per molecule. It catalyzes, nonstereospecifically, several oxidations in the alkyl side chains of lignin-related compounds: C α —C β cleavage in lignin-related compounds of the type aryl—C α HOH—C β HR—C γ H 2 OH (R = -aryl or - O -aryl), oxidation of benzyl alcohols to aldehydes or ketones, intradiol cleavage in phenylglycol structures, and hydroxylation of benzylic methylene groups. It also catalyzes oxidative coupling of phenols, perhaps explaining the long-recognized association between phenol oxidation and lignin degradation. All reactions require H 2 O 2 . The C α —C β cleavage and methylene hydroxylation reactions involve substrate oxygenation; the oxygen atom is from O 2 and not H 2 O 2 . Thus the enzyme is an oxygenase, unique in its requirement for H 2 O 2 .