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Biodegradation of Lignin
Published in Jean-Luc Wertz, Magali Deleu, Séverine Coppée, Aurore Richel, Hemicelluloses and Lignin in Biorefineries, 2017
Jean-Luc Wertz, Magali Deleu, Séverine Coppée, Aurore Richel
Cellobiose dehydrogenase (CDH) (cellobiose:acceptor 1-oxidoreductase; EC 1.1.99.18), an extracellular protein, is produced in a number of wood- and cellulose-degrading fungi, including basidiomycetes (mostly white-rot fungi) and ascomycetes, growing on cellulosic medium.1,52 CDH is a monomeric enzyme containing an N-terminal heme domain and a C-terminal flavin domain.52 This enzyme catalyzes the two-electron oxidation of cellobiose and more generally cellodextrins, mannodextrins, and lactose to the corresponding lactones. Oxidation takes place in the flavin domain where electrons are transferred to flavin adenine dinucleotide (FAD) and redistributed using electron acceptors such as dioxygen, quinones, phenoxy radicals, or a subsequent one-electron transfer to the heme domain. The heme part is also involved in electron transfer to a wide variety of substrates acting as electron acceptors including quinones, metal ions, and organic dyes. Reduced heme iron may reduce dioxygen to hydrogen peroxide or participate in Fenton reaction.
Hydrolysis and Fermentation Technologies for Alcohols
Published in Yatish T. Shah, Water for Energy and Fuel Production, 2014
There are mechanistically and structurally different types of cellulases. Each cellulolytic microbial group has an enzyme system unique to it. The capabilities of enzyme can vary from hydrolysis of soluble derivatives of cellulose to disrupting the cellulose complex. Cellulase is actually composed of a number of distinctive enzymes based on the specific types of reactions catalyzed. In fact, cellulase can be characterized into five general groups: Endocellulase cleaves the internal bonds to disrupt the crystalline structure of cellulose and expose individual polysaccharide chains.Exocellulase detaches two or four saccharide units from the ends of exposed chains produced by endocellulase, resulting in the production of disaccharides or tetrasaccharides, such as cellobiose. There are two principal types of exocellulases or cellobiohydrolases (CBHs): (1) CBH-I that works processively from the reducing end and (2) CBH-II that works processively from the nonreducing end of cellulose. Here the processivity implies the ability of enzyme to continue repetitively its catalytic function without dissociating from its substrate. The chance for reaction is significantly increased by an active enzyme adsorbed onto the surface of the substrate.Beta-glucosidase or cellobiase hydrolyzes the disaccharides and tetrasac-charides into individual monosaccharides.Oxidative cellulase depolymerizes cellulose by the free radical reactions as in the case of a cellobiose dehydrogenase (acceptor), an enzyme that catalyzes the dehydrogenation of cellobiose.Cellulose phosphorylase depolymerizes cellulose using phosphates instead of water.
An overview of cotton and polyester, and their blended waste textile valorisation to value-added products: A circular economy approach – research trends, opportunities and challenges
Published in Critical Reviews in Environmental Science and Technology, 2022
Karpagam Subramanian, Manas Kumar Sarkar, Huaimin Wang, Zi-Hao Qin, Shauhrat S. Chopra, Mushan Jin, Vinod Kumar, Chao Chen, Chi-Wing Tsang, Carol Sze Ki Lin
In addition to glycoside hydrolases that are commonly used in the textile industry to act on cotton fabrics, many oxidative enzymes could potentially play important roles in textile modification and pretreatment processes. For instance, lytic polysaccharide monooxygenases (LPMOs) are a newly discovered class of copper-dependent oxygenases that are used to degrade recalcitrant polysaccharides on crystalline surfaces. These enzymes are therefore considered as a breakthrough in the field, as oxidative cleavage of the glycosidic linkages catalyzed by LPMOs makes the substrate more susceptible to subsequent hydrolysis steps (Lo Leggio et al., 2015). Four classes of LPMOs are known so far, and they have been classified as auxiliary activity (AA) enzymes, of which AA9 LPMOs are exclusively found in fungi and preferably used to oxidize cellulose (Beeson et al., 2015). With the help of electron donors including ascorbate, pyrogallol or accessory proteins such as cellobiose dehydrogenase, the cellulose fiber structure can be ruptured by creating nicking points that weaken the fiber cohesion (Villares et al., 2017). Because of this catalytic feature, cotton linters, an important by-product of the textile industry, can be upgraded to nanofibrillated cellulose (NFC) using cellulases in synergy with LPMOs (Valls et al., 2019). Moreover, the mechanical properties of this nanomaterial can be further improved by using laccases, a type of oxidase that can create new functional groups in cellulose.
Potential strategies to prevent encrustations on urinary stents and catheters – thinking outside the box: a European network of multidisciplinary research to improve urinary stents (ENIUS) initiative
Published in Expert Review of Medical Devices, 2021
Ali Abou-Hassan, Alexandre Barros, Noor Buchholz, Dario Carugo, Francesco Clavica, Petra de Graaf, Julia de La Cruz, Wolfgang Kram, Filipe Mergulhao, Rui L Reis, Ilya Skovorodkin, Federico Soria, Seppo Vainio, Shaokai Zheng
In the case of urinary catheters and stents, enzymes can be immobilized onto the surfaces either reversibly or irreversibly. Reversible immobilization includes methods through which the enzymes can be easily removed [15,16]. However, irreversible methods are generally preferred because of the improved stability and lower extent of leaching [4]. Urological trials with antimicrobial enzyme coating are still in the early stages. It was demonstrated that in vitro, a cellobiose dehydrogenase (CDH)/cellobiose stent coating inhibited several urinary pathogens including MRSA by generating H2O2, thus demonstrating an ability to kill microbes on demand when biofilms were formed [17]. Also, stent coatings with oxalate-degrading enzymes were trialed in vitro [18] and in an animal study [19]. Encrustation often results from the deposition of calcium oxalate on the biomaterial surface. A commensal colonic bacterium oxalobacter formigenes produces several oxalate-degrading enzymes, which, when used as a coat on silicone, resulted in an up to 53% reduction in encrustation with no apparent toxicity [18,19].
Analysis of polysaccharide hydrolases secreted by Aspergillus flavipes FP-500 on corn cobs and wheat bran as complex carbon sources
Published in Preparative Biochemistry & Biotechnology, 2020
Lizzete Ruth Torres-Barajas, María Teresa Alvarez-Zúñiga, Guillermo Mendoza-Hernández, Guillermo Aguilar-Osorio
Despite the differences in the composition of complex substrates used in the cultivation of A. flavipes FP-500, there are 22 proteins that were found to be present on both substrates regardless of the carbon source used (Figure 3c), suggesting that they are essential for the fungus to degrade the targeted polysaccharides of both residues. During the growth of A. flavipes FP-500 four endo-1,4-β-xylanases, two β-glucosidases, two cellobiose dehydrogenase, two endoglucanases, cellobiohydrolase, β-galactosidase, arabino endo 1,5-α-arabinosidase, α-L-arabinofuranosidase, N-O-diacetylmuramidase, feruloyl esterase, acetyl xylan esterase, extracellular GDS-like lipase, carboxypeptidase, aspergillopepsin, and two uncharacterized proteins were found. These results are comparable with Lu et al.[59] They show that A. niger produced the same enzymes when it grows on xylose.