Laccase-mediator catalyzed conversion of model lignin compounds

Modification of Deoxynivalenol by a Fungal Laccase Paired with Redox Mediator TEMPO

Mycotoxins such as deoxynivalenol introduce a health risk to the food supply and are costly to manage or avoid. Technologies for reducing or eliminating the toxicity of deoxynivalenol could be useful in a variety of processes, such as in preserving the value as animal feed of byproducts of ethanol production. We characterized transformation products of deoxynivalenol that were formed by the combination of a fungal laccase paired with the chemical mediator 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO), using chromatography, mass spectrometry, and nuclear magnetic resonance spectroscopy. Alcohol groups at the C3 and C15 positions of deoxynivalenol were oxidized to ketones, and the chemical mediator became covalently linked to the C4 position. Conditions experienced during gas chromatography led to the dissociation of TEMPO, forming 3,15-diketodeoxynivalenol. Understanding the range of possible modifications to deoxynivalenol and other trichothecenes is a necessary step toward effective remediation of contaminated grain.

Isothermal titration calorimetric assessment of lignin conversion by laccases

Lignin valorization may offer a sustainable approach to achieve a chemical industry that is not completely dependent on fossil resources for the production of aromatics. However, lignin is a recalcitrant, heterogeneous, and complex polymeric compound for which only very few catalysts can act in a predictable and reproducible manner. Laccase is one of those catalysts and has often been referred to as an ideal “green” catalyst, as it is able to oxidize various linkages within lignin to release aromatic products, with the use of molecular oxygen and formation of water as the only side product. The extent and rate of laccase‐catalyzed lignin conversion were measured using the label‐free analytical technique isothermal titration calorimetry (ITC). IITC provides the molar enthalpy of the reaction, which reflects the extent of conversion and the time‐dependent power trace, which reflects the rate of the reaction. Calorimetric assessment of the lignin conversion brought about by various fungal and bacterial laccases in the absence of mediators showed marked differences in the extent and rate of conversion for the different enzymes. Kraft lignin conversion by Trametes versicolor laccase followed Michaelis–Menten kinetics and was characterized by the following thermodynamic and kinetic parameters ΔH_ITC = −(2.06 ± 0.06)·10³ kJ mol⁻¹, K_M = 6.6 ± 1.2 μM and V_max = 0.30 ± 0.02 U/mg at 25°C and pH 6.5. We envision calorimetric techniques as important tools for the development of enzymatic lignin valorization strategies.

Enzymatic bioconversion process of lignin: mechanisms, reactions and kinetics

Lignin is a wasted renewable source of biomass-derived value-added chemicals. However, due to its material resistance to degradation, it remains highly underutilized. In order to develop new, catalysed and more environment friendly reaction processes for lignin valorization, science has turned a selective concentrated attention to microbial enzymes. This present work looks at the enzymes involved with the main reference focus on the different elementary mechanisms of action/conversion rate kinetics. Pathways, like with laccases/peroxidases, employ radicals, which more readily result in polymerization than de-polymerization. The β-etherase system interaction of proteins targets β-O-4 ether covalent bond, which targets lower molecular weight product species. Enzymatic activity is influenced by a wide variety of different factors which need to be considered in order to obtain the best functionality and synthesis yields.

Improving laccase production from Trametes versicolor using lignocellulosic residues as cosubstrates and evaluation of enzymes for blue wastewater biodegradation

Biocatalytic degradation of recalcitrant pollutants employing ligninolytic enzymes is a promising approach for wastewater treatment. However, enzymes production must be improved to make biodegradation a more cost-effective treatment. In this research, laccase production from Trametes versicolor using lignocellulosic residues (agave bagasse, coconut fibers and wheat bran) as cosubstrates was improved using a central composite face-centered design, and the application of the enzymes-rich culture supernatant was evaluated for blue wastewater biodegradation. Findings revealed that the optimal conditions for laccase production were found at 35 °C and 5 g/L of wheat bran as cosubstrate, reaching about 200 U/mL in 11 days in a batch submerged fermentation. These conditions were scaled up for a submerged fermentation using an airlift reactor, and a maximum enzymatic activity of 1200 U/mL was achieved in 9 days at 30 °C. This enzymes-rich culture supernatant was tested for the degradation of blue wastewater from aircraft in an airlift reactor. Results showed a COD removal efficiency of 43% and an increase of the biodegradability index from 0.64 to 1.36, both results applying an enzymatic activity of supernatant of 300 U/mL. In conclusion, the enzymatic biodegradation becomes a viable strategy for the pretreatment of a real effluent such as the blue wastewater collected in public transportation.

Cultivation of Mushrooms and Their Lignocellulolytic Enzyme Production Through the Utilization of Agro-Industrial Waste

A large amount of agro-industrial waste is produced worldwide in various agricultural sectors and by different food industries. The disposal and burning of this waste have created major global environmental problems. Agro-industrial waste mainly consists of cellulose, hemicellulose and lignin, all of which are collectively defined as lignocellulosic materials. This waste can serve as a suitable substrate in the solid-state fermentation process involving mushrooms. Mushrooms degrade lignocellulosic substrates through lignocellulosic enzyme production and utilize the degraded products to produce their fruiting bodies. Therefore, mushroom cultivation can be considered a prominent biotechnological process for the reduction and valorization of agro-industrial waste. Such waste is generated as a result of the eco-friendly conversion of low-value by-products into new resources that can be used to produce value-added products. Here, we have produced a brief review of the current findings through an overview of recently published literature. This overview has focused on the use of agro-industrial waste as a growth substrate for mushroom cultivation and lignocellulolytic enzyme production.

Enzymatic hydrolysis of lignin by ligninolytic enzymes and analysis of the hydrolyzed lignin products

The degradation of alkali lignin was studied using three types of pure enzyme, Lac, LiP, and MnP, using alkali lignin as substrate. The alkali lignin removal rate was found to be 28.98% when Lac, LiP, and MnP were cultured together for alkali lignin degradation. Changes in the structure and composition before and after degradation were characterized by scanning electron microscopy, Fourier-transform infrared spectroscopy, nitrogen adsorption, and gas chromatography-mass spectrometry. The degradation product pathways were analyzed. The enzyme was proven to degrade alkali lignin, resulting in destruction of the alkali lignin structure, ring-opening of the macromolecular benzene ring structure and groups in alkali lignin, and chemical bond cleavage. This study explains the principle of alkali lignin enzymatic hydrolysis and provides a theoretical basis for the biodegradation of lignin.

Laccase catalysis for the synthesis of bioactive compounds

The demand for compounds of therapeutic value is increasing mainly because of new applications of bioactive compounds in medicine, pharmaceutical, agricultural, and food industries. This has necessitated the search for cost-effective methods for producing bioactive compounds and therefore the intensification of the search for enzymatic approaches in organic synthesis. Laccase is one of the enzymes that have shown encouraging potential as biocatalysts in the synthesis of bioactive compounds. Laccases are multicopper oxidases with a diverse range of catalytic activities revolving around synthesis and degradative reactions. They have attracted much attention as potential industrial catalysts in organic synthesis mainly because they are essentially green catalysts with a diverse substrate range. Their reaction only requires molecular oxygen and releases water as the only by-product. Laccase catalysis involves the abstraction of a single electron from their substrates to produce reactive radicals. The free radicals subsequently undergo homo- and hetero-coupling to form dimeric, oligomeric, polymeric, or cross-coupling products which have practical implications in organic synthesis. Consequently, there is a growing body of research focused on the synthetic applications of laccases such as organic synthesis, hair and textile dyeing, polymer synthesis, and grafting processes. This paper reviews the major advances in laccase-mediated synthesis of bioactive compounds, the mechanisms of enzymatic coupling, structure-activity relationships of synthesized compounds, and the challenges that might guide future research directions.