Oxidation lignin peroxidase

Hammel KE, MD Mozuch, KA Jensen, PJ Kersten (1994) HjOj recycling during oxidation of the arylglycerol P-aryl ether lignin structure by lignin peroxidase and glyoxal oxidase. Biochemistry 33 13349-13354. 

Vazquez-Duhalt, R. Westlake, D. W. S., and Fedorak, P. M., Lignin Peroxidase Oxidation of Aromatic-Compounds in Systems Containing Organic-Solvents. Applied and Environmental Microbiology, 1994. 60(2) pp. 459-466. 

Lignin peroxidase, secreted by the white-rot fungus Phanerochaete chrysosporium in response to nutrient deprivation, catalyzes the H202-dependent oxidation of non-phenolic aromatic substrates. The present report summarizes the kinetic and structural characteristics of lignin peroxidase isozymes. Our results indicate that the active site of lignin peroxidase is more electron deficient than other peroxidases. As a result, the redox potential of the heme active site is higher, the heme active site is more reactive and the oxycomplex is more stable than that of other peroxidases. Also discussed is the heme-linked ionization of lignin peroxidase. 

Mn-dependent peroxidase differs from lignin peroxidase in that it utilizes Mn (II) as the main substrate (74). The oxidized manganese ion, Mn (III), carries out the oxidation of organic molecules. Compound I of Mn-dependent peroxidase is able to oxidize Mn (II) to Mn (III) as well as some phenolic compounds the compound II can only oxidize Mn (II) (14) ... 

Effect of pH on Lignin Peroxidase Catalysis. The oxidation of organic substrates by lignin peroxidase (Vmax) has a pH optimum equal to or possibly below 2. Detailed studies have been performed on the pH dependency of many of the individual reactions involved in catalysis. The effect of pH on the reaction rates between the isolated ferric enzyme, compounds I or II and their respective substrates has been studied. Rapid kinetic data indicate that compound I formation from ferric enzyme and H2O2 is not pH dependent from pH 2.5-7.5 (75,16). Similar results are obtained with Mn-dependent peroxidase (14). This is in contrast to other peroxidases where the pKa values for the reaction of ferric enzyme with H2O2 are usudly in the range of 3 to 6 (72). 

Although compound I formation is not influenced by pH, reactions of compounds I and II are significantly affected by pH. These reactions are acid-catalyzed 16,17). The rate constant for the oxidation of veratryl alcohol or fenocyanide by lignin peroxidase compound I is 10 times greater at pH 3.5 than at pH 6.0. The enhancement in rate is of the same magnitude for compound II reacting with veratryl alcohol. Therefore, the observed pH dependency for Vmax in catalysis is due to the pH-dependent reactions between the compounds I and n and the reducing substrates. 

Activity Assays. The standard activity assay mixture of 3 ml contained about 0.1 U/ml lignin peroxidase, 0.4 mM veratryl alcohol (Fluka, purum >97%) and 0.1M sodium tartrate, pH 3.0. The reaction was started by adding 15 fil of 54 mM H2O2 to make a final concentration of 0.28 mM in the reaction. The production of veratraldehyde was followed by recording the change of absorbance for 12 seconds at 310 nm in a cuvette which was thermostated to 37°C. The reaction was started 24 seconds before the recording. One unit of lignin peroxidase is defined as the amount of enzyme required to oxidize one imol of veratryl alcohol to veratraldehyde in one minute. 

These findings led to the proposition that the veratryl alcohol is degraded via the quinone intermediates (Figure 5) to CO2 through a series of transformations involving lignin peroxidase, perhydroxy radicals and the NADP-dependent aryl alcohol oxidoreductase. Veratraldehyde, the major product of lignin peroxidase catalyzed veratryl alcohol oxidation, is rapidly reduced back to veratryl alcohol it is the further metabolism of the side products of the oxidative process, viz. the quinones and lactones, that drives the overall transformation towards completion (34). 

In plant cell walls, lignin monomers seem to be present in vivo in the form of cinnamyl alcohols. In vitro, their acid precursors can also be oxidized by peroxidases (3). In order to gain further insight into the possible... 

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