Abstract
The extracellular lignin peroxidase from the white-rot basidiomycete Phanerochaete chrysosporium is thought to play an important role in lignin biodegradation. However, the majority of lignin-derived preparations actually experience overall polymerization at the hands of the enzyme in vitro. It has now been found that, in the presence of H2O2 at pH 4.0, the monomeric lignin precursor coniferyl alcohol is polymerized quantitatively by a lignin peroxidase preparation which is uncontaminated with MnII-dependent peroxidases. 13C NMR spectrometry of the resulting dehydropolymerisates from 13C-labeled monolignols confirms that the frequencies of different interunit linkages are very similar to those engendered through the action of horseradish peroxidase with H2O2. Indeed, lignin peroxidase does not ultimately seem to be a prerequisite for lignin degradation in vivo, yet its activity can still accelerate the conversion of lignin-derived preparations by P. chrysosporium to CO2. Consequently, lignin peroxidase can provisionally be expected to fulfill two important functions. On the one hand, the enzyme may detoxify lower molecular weight phenolic compounds released from lignins during their fungal decomposition. On the other hand, through the introduction of suitable functional groups, lignin peroxidase could indirectly enhance the susceptibility of macromolecular lignin structures toward depolymerization by another enzyme.
Highlights
From the §Departmentsof Wood Science and Biochemistry, Virginia Polytechnic Instituteand State University, Blacksburg, Virginia 24061 and the $Department of Forest Products, University of Minnesota, St
- 3 titatively by a lignin peroxidase preparation which is uncontaminated with Mn”-dependentperoxidases. 13C NMR spectrometry of the resulting dehydropolymerisates from 13C-labeledmonolignols confirms that the
A similar procedure was separately carried out with [2-13C]coniferyl Partial Purification of Lignin Peroxidase Isozymes: Isoelecalcohol 2b (96atom % 13C)to afford a light-beigedehydropolymerized tric Focusing and ProteinlActiuity Staining-Following conproduct in quantitative yield
Summary
A similar procedure was separately carried out with [2-13C]coniferyl Partial Purification of Lignin Peroxidase Isozymes: Isoelecalcohol 2b (96atom % 13C)to afford a light-beigedehydropolymerized tric Focusing and ProteinlActiuity Staining-Following conproduct in quantitative yield. Coniferyl alcohol 2 (30.66 mg, 0.17 mmol) was activity [26], five brown bands appeared that seemed to codissolved in sodium tartrate buffer (25 mM, 25 ml, pH 4.0 at room temperature) as in solution A described above. An aliquot (2 sections, upon being immersed separatelyin the mixtures, revealed the presenceof six bands that stained faintlyyellow 62.9, and 70.8 ppm (Fig. l a andTable 11, part la) The in both cases, so that no Mn”-dependentenzymes were pres- corresponding product derived from [2-13C]coniferylalcohol ent. Activity in LigninPeroxidase Preparation-Inestablishing from [3-’3C]coniferyl alcohol 2c, the solution-state I3C NMR whether phenol red oxidation was influenced by any Mn”- spectrum displayedsignals at 71.1,71.7,85-87, and 128.9 dependent peroxidases in thedialyzed lignin peroxidaseprep- ppm, respectively (Fig. 3a and Table, part 3a). Temperature) was deliveredat the same rate(0.52 ml/h for 48 h) over the same timeperiod
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