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Lignin-modifying enzymes benefit industry as they can break down lignin; a common waste product of the paper and pulp industry. These enzymes have been used in the refinement of poplar as lignin inhibits the enzymatic hydrolysis of treated poplar and Lignin-modifying enzymes can efficiently degrade the lignin thus fixing this problem. [4]
For example, laccases play a role in the formation of lignin by promoting the oxidative coupling of monolignols, a family of naturally occurring phenols. [1] [2] Other laccases, such as those produced by the fungus Pleurotus ostreatus, play a role in the degradation of lignin, and can therefore be classed as lignin-modifying enzymes. [3]
Lignin is found to be degraded by enzyme lignin peroxidases produced by some fungi like Phanerochaete chrysosporium. The mechanism by which lignin peroxidase (LiP) interacts with the lignin polymer involves veratrole alcohol, which is a secondary metabolite of white rot fungi that acts as a cofactor for the enzyme.
In contrast to fungi, most bacterial enzymes involved in lignin degradation are intracellular, including two classes of DyP and most bacterial laccases. [34] In the environment, lignin can be degraded either biotically via bacteria or abiotically via photochemical alteration, and oftentimes the latter assists in the former. [38]
Production of lignin-peroxidase and manganese-peroxidase is the hallmark of basidiomycetes and is often used to assess basidiomycete activity, especially in biotechnology applications. [38] Most white-rot species also produce laccase, a copper-containing enzyme that degrades polymeric lignin and humic substances. [39]
The systematic name of this enzyme class is Mn(II):hydrogen-peroxide oxidoreductase. Other names in common use include peroxidase-M2, and Mn-dependent (NADH-oxidizing) peroxidase. It employs one cofactor, heme. This enzyme needs Ca 2+ for activity. White rot fungi secrete this enzyme to aid lignin degradation.
The low enzymatic hydrolysis can be attributed to lignin, which blocks enzyme access to the cellulose. There are several ways of reducing the effects of lignin on enzymatic hydrolysis, one of which is the use of surfactant additives.
Lignin is a macromolecule formed from the combination of many phenolic aromatic groups via oxidative coupling. Because of its high stability, lignin is incapable of being broken down through simple decomposition. As a result, white-rot fungi employ a series of enzymes that break lignin down into smaller aromatic rings.
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