Catalyzed by lignin peroxidase

Side-Chain Cleavage Reactions of 0-1 and fl-O-4 Lignin Model Compounds Catalyzed by Lignin Peroxidase. 

Thus, most of the degradative reactions of polymeric lignins suggested previously by the analysis of decayed lignin isolated from decayed wood by white-rot fungi were catalyzed by lignin peroxidase. 

Renganathan V, Miki K, Gold MH (1987) Haloperoxidase Reactions Catalyzed by Lignin Peroxidase, an Extracellular Enzyme from the Basidiomycete Phanerochaete chrysospo-rium. Biochemistry 26 5127... 

Fig. 8.8 Proposed mechanism for the dioxin oxidation catalyzed by lignin peroxidase [117]...

Figure 4. Reactions catalyzed by lignin peroxidase. Me = methyl, Et = ethyl.

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. 

Lignin is formed by the dehydrogenative polymerization of coniferyl, sinapyl, and p-coumaryl alcohol, which is catalyzed by a peroxidase and requires H2O2. A section of the structure of lignin formed by the polymerization of coniferyl alcohol is shown in Fig. 18.5. Lignins strengthen the walls of plant cells. They play a role as fiber in foods (cf. 15.2.4.2). 

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. 

Lignin peroxidase of Phanerochaete chrysosporium catalyzes the ring cleavage of /3-0-4 lignin substructure model compounds and synthetic lignin (DHP). A mechanism for the ring cleavage by the enzyme is described. 

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