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

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Abstract
An extracellular lignin-degrading enzyme from the basidiomycete P. chrysosporium Burdsall was purified to homogeneity by ion-exchange chromatography. The 42,000-dalton ligninase contains 1 protoheme IX per molecule. It catalyzes, nonstereospecifically, several oxidations in the alkyl side chains of lignin-related compounds: C.alpha..sbd.C.beta. cleavage in lignin model compounds of the type aryl .sbd.C.alpha.HOH.sbd.C.beta.HR.sbd.C.gamma.H2OH (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 H2O2. The C.alpha..sbd.C.beta. cleavage and methylene hydroxylation reactions involve substrate oxygenation; the oxygen atom is from O2 and not H2O2. Thus, the enzyme is an oxygenase, unique in its requirement for H2O2.