China
Africa
Explore chapters and articles related to this topic
Laccase-Mediated Synthesis of Novel Antibiotics and Amino Acid Derivatives
Published in Peter Grunwald, Pharmaceutical Biocatalysis, 2019
The laccase reactions proceed by formation of a radical cation, with subsequent deprotonation of the hydroxy group to give a radical (Fig. 8.1). Catalytic cycle of laccase-mediated substrate oxidation.
Laccase
Published in René Lontie, Copper Proteins and Copper Enzymes, 1984
Laccase is a blue copper-containing oxidase which is widely distributed in higher plants and fungi. It belongs to a small group of blue oxidases which can utilize the full oxidizing capacity of dioxygen and reduce it to two molecules of water. The other enzymes are the blue proteins ceruloplasmin and ascorbate oxidase which have many properties in common with laccase. They will, however, not be considered here since they are treated in separate chapters in this volume.
The Reactivity Of Copper Sites In The “Blue” Copper Proteins
Published in René Lontie, Copper Proteins and Copper Enzymes, 1984
The reactivity of the different copper sites present in blue copper oxidases (cf. Appendix 1) is naturally determined by their different functional roles.5 The catalytic cycle of these oxidases involves the uptake of single electrons from their respective substrates and reduction of dioxygen with four electrons to water. In this cycle the blue oxidases employ three different types of copper sites, all endowed by unique chemical or spectroscopic properties: the type-1 blue copper site described in Section I; the type-2 copper site, characterized by unusual chemical reactivity yet with spectral properties similar to low Μr copper complexes; and type-3 copper, with two copper ions in a binuclear site. In their oxidized Cu(II) state, the latter two are antiferromagnetically coupled so that they are undetected by EPR or magnetic susceptibility measurements. Three enzymes constitute the group of blue oxidases: the laccases, ascorbate oxidase, and ceruloplasmin. Each of these proteins contain all three types of copper sites. The first ones contain just one of each type, while the two other contain several.5,73 In the following we shall consider the reactivity of each of the different types of copper sites present in these oxidases. The most intensely studied blue copper oxidase is laccase from the Japanese lacquer tree R. vernicifera. This extracellular, water-soluble enzyme contains four copper atoms bound to the three distinct sites, mentioned above.
Induced mutation in Agaricus bisporus by gamma ray to improve genetic variability, degradation enzyme activity, and yield
Published in International Journal of Radiation Biology, 2021
Tayebeh Harfi, Motallebi-Azar Alireza, Rasouli Farzad, Zaare-Nahandi Fariborz
To assay the activity of extracellular lignin degrading-enzymes, 2g of each substrate was picked up after complete spawn running, ground completely using liquid nitrogen, and after adding 4ml of sodium acetate buffer (0.1M and pH: 4.50), was centrifuged at 12,000rpm at 4 °C for 20min. Two ml of the supernatant was then separated as an extract for the enzyme activity assay (Khammuang and Sarnthima 2007). Laccase activity was measured according to Shin and Lee (2000), with minor modifications based on ABTS oxidation as the substrate (Khammuang and Sarnthima 2007). The spectroscopic assay was performed at 421nm using a spectrophotometer (Spekol1500). The enzyme activity was calculated as U. ml−1 using an ATBS extinction coefficient of 36,000M−1cm−1. Manganese peroxidase activity was measured according to Bonnen et al. (1994), based on Guaiacol oxidation as the substrate. The spectroscopic assay was performed at 465nm and the enzyme activity was calculated as U ml−1 based on a Guaiacol extinction coefficient of 12,100M−1cm−1.
Oxy-PAHs: occurrence in the environment and potential genotoxic/mutagenic risk assessment for human health
Published in Critical Reviews in Toxicology, 2019
Adeline Clergé, Jérémie Le Goff, Claire Lopez, Jérôme Ledauphin, Raphaël Delépée
PAKs and PAQs were also detected in soils (Niederer 1998; Brooks et al. 1999; Meyer et al. 1999; Eriksson et al. 2000; Lundstedt et al. 2003; Lundstedt, Haglund et al. 2006; Lundstedt, Persson et al. 2006; Mattsson, Lundstedt, and Stenius 2009; Layshock, Wilson, and Anderson 2010). When oxy-PAHs are deposited on soil, they possibly become mobile. Direct transfer from atmospheric and aquatic compartments can occur by particulate matter deposition or water spreading, respectively. In soil, most of oxy-PAHs are bound to soil particles and their mobility will be influenced by the mobility of these particles. However, oxy-PAHs and mainly PAQs can also be produced in situ during the bioremediation of soil contaminated with hazardous organic compounds and degradation of PAHs can be accompanied by the accumulation of PAH metabolites. Some authors have worked on treatment of natural or artificial PAHs-contaminated soils thanks to different methods (white-rot fungi, Fenton oxidation …). Degradation of parent PAHs induces formation of some nitro-PAHs, alkyl-PAHs, hydroxy-PAHs and oxy-PAHs such as 9,10-anthraquinone (9,10-AQ), 9-FLU, and 4-hydroxy-9-fluorenone (Andersson and Henrysson 1996; Wischmann and Steinhart 1997; Lee et al. 1998; Eriksson, Dalhammar, and Borg-Karlson 2000; Lee and Hosomi 2001; Meyer and Steinhart 2001; Andersson et al. 2003; Lundstedt et al. 2003; Lundstedt, Haglund et al. 2006). Accumulation of 9-FLU and BAQ following microbial degradation of PAHs has been described (Andersson et al. 2003). This accumulation may result in an increase of soil toxicity and/or a more persistent toxicity in time, even though parent PAHs are degraded. All these studies demonstrate that many PAKs and PAQs can accumulate in the soil during PAHs degradation thereby creating new environmental pollutants. The production process of oxy-PAHs from PAHs in microbial or fungal organisms has been described. Enzymatically, this process involves oxygenase, dehydrogenase and lignolytic enzymes. For example, it has been shown that laccase is a fungal lignolytic enzyme which is implicated in microbial catabolism of PAHs to form PAQs (Haritash and Kaushik 2009).