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Bioremediation of Hydrocarbons and Classic Explosives: An Environmental Technology Removing Hazardous Wastes
Published in Vivek Kumar, Rhizomicrobiome Dynamics in Bioremediation, 2021
This reduction is referred to as type first, this reaction type is independent of O2 molecule, and no radicals are formed. The nitrite reductase enzymes are able to carry out this electronic duplex donation by reduced pyridine nucleotides. This also includes other reduction reactions carried out by enzymes that reduce nitro aromatic compounds. The main enzymes include dihydrolipic amide dehydrogenase, aldehyde oxidase, xanthine oxidase, diaphorases, CO dehydrogenase and hydrogenases. The nitro group could also be reduced in vitro via single-electron transfer, which forms a nitro anion radical. This radical is an alleged intermediate in reducing a nitro group to a nitroso group. But it can react with O2 molecule to generate a superoxide anion and modify the original nitro aromatic compound. The enzymes which carry out this reaction are known as O2-sensitive (type II) nitro reductases and are observed in bacteria such as Escherichia coli and Clostridium spp. (Roldán et al. 2008). Abiotic reduction could also happen for nitro groups to the corresponding amines in aquifers, soils and sediments. There are numerous probable electron donors in natural system, such as sulphur and iron reducing microbial species, and also in natural organic materials, which may be reduced from nitro aromatic compounds through biological degradation. TNT reacts with siloxane surface of clays to create covalent groups. Alive organisms play a significant role in these biological processes but they are yet to be explored to understand properly (Gh and Moussa 2011, Spain 1995).
Metabolism and Toxicity of Occupational Neurotoxicants: Genetic, Physiological, and Environmental Determinants
Published in Lucio G. Costa, Luigi Manzo, Occupatinal Neurotoxicology, 2020
Stefano M. Candura, Luigi Manzo, Anna F. Castoldi, Lucio G. Costa
Alcohols, aldehydes, and ketones are functional groups of many occupational neurotoxicants. Moreover, they often occur from oxidative or hydrolytic metabolic reactions. These functional groups may be biotransformed by several soluble enzymes, such as alcohol dehydrogenase (ADH), aldehyde oxidase, aldehyde dehydrogenase (ALDH), and aldehyde/ketone reductases.1 These enzymatic systems are present in a number of mammalian tissues. Since alcohol, aldehyde, or ketone groups often confer pharmaco/toxicological properties, their oxidation or reduction generally represents a detoxication pathway. There are, however, exceptions. For example, ADH, a cytosolic NAD-dependent enzyme located primarily in the liver, oxidizes ethanol to acetaldehyde (Figure 4A), which contributes to ethanol toxicity. To a minor extent, conversion of ethanol to acetaldehyde is also carried out by the microsomal ethanol oxidizing system (MEOS), which involves CYP2E1, and by cytosolic catalase, which uses hydrogen peroxide (H202) to perform the oxidation. Acetaldehyde is in turn oxidized to acetic acid by ALDH (Figure 4A), which is another cytosolic (in humans) NAD-requiring enzyme. Finally, acetic acid enters the Krebs cycle (as acetyl-CoA), and is degradated to C02 and water.
Enzyme Kinetics and Drugs as Enzyme Inhibitors
Published in Peter Grunwald, Pharmaceutical Biocatalysis, 2019
The metabolic reactions leading to the biotransformation of drugs is a field of major importance in drug discovery. Most drugs (70–80% of all drugs in clinical use; Zanger and Schwab, 2013; see also Xie et al., 2016) are metabolized by P450 (CYP) enzymes. Of the many P450 enzymes only members of the CYP1, 2, and 3 families are involved among them CYPs 3A4, 2C9, 2C8, 2E1, and 1A2. Other enzyme classes involved in drug metabolism are mainly glucuronosyltransferases and hydrolases but to a lesser extent also carbonyl reductases and aldehyde oxidase (Cerny, 2016). Efficacy and toxicity of drugs depends on interindividual genetic variations in drug metabolizing enzymes caused by various mechanisms including genetic polymorphisms, induction by xenobiotics, regulation by cytokines, hormones, sex and age, disease states and others. A useful contribution to the study of individual responses to medication based on genomic information comes from pharmacogenomics (Ahmed et al., 2016). Drug-metabolizing enzymes are treated in separate chapters (Volumes 4 and 6 of this Series).
Oxovanadium and dioxomolybdenum complexes: synthesis, crystal structure, spectroscopic characterization and applications as homogeneous catalysts in sulfoxidation
Published in Journal of Coordination Chemistry, 2021
Hadi Kargar, Azar Kaka-Naeini, Mehdi Fallah-Mehrjardi, Reza Behjatmanesh-Ardakani, Hadi Amiri Rudbari, Khurram Shahzad Munawar
Molybdenum is an essential element, present in more than 40 different naturally occurring enzymes involved in redox reactions. It is important for the fixation and assimilation of atmospheric nitrogen with the help of bacterial nitrogenase and nitrate reductase [24]. Moreover, molybdoenzymes, sulfite oxidase and aldehyde oxidase are used for oxidation of sulfite and aldehyde, respectively [25]. In addition to the importance of molybdenum complexes in biological process, they have potential to be used as effective catalyst in epoxidation of olefins (styrene and cyclohexane), olefin metathesis, isomerization of allylic alcohol, oxidation of sulfides to sulfoxides and oxidation of amines [26–28]. Coordination of molybdenum with the aroylhydrazones usually generates MoO2L or MoOL complexes which bear one or two open sites that can be used to enhance the coordination number by binding with substrate molecules. Due to the presence of these vacant sites molybdenum complexes can be regarded as template for numerous enzymatic and catalytic sites [29, 30].
Remediation of 2,4,6-trinitrotoluene Persistent in the Environment – A review
Published in Soil and Sediment Contamination: An International Journal, 2020
TNT can be degraded by biological agents which include microorganisms, fungi and yeasts that have the capability of transforming TNT into non-toxic end products (Serrano-Gonzalez. et al. (2018). A wide variety of bacterial isolates such as Pseudomonas sp.,Desulfovibrio sp., Bacillus sp. and Staphylococcus sp. have the ability to transform TNT under aerobic and anaerobic conditions through reductive pathways (McFarlan, Sara, and Yao 2016). However, anaerobic consortia have been reported to be more effective than pure cultures of the aerobes. Either aerobic or anaerobic, biotransformation is typically co-metabolic in nature. The reduction pathway results in the formation of nitroso, hydroxylamino and amino derivatives of TNT via a series of electron transfers. Oxygen insensitive enzymes (Type I) such as nitroreductase, aldehyde oxidase, dihydrophilic amide dehydrogenase aid in the reduction process (Nyanhongo et al. 2005). The derivatives formed through this process are equally harmful to humans and environment unless complete reduction to the amino group occurs. Another class of enzymes, oxygen sensitive (Type II) enzymes prevalent in Clostridium sp. and E. coli sp. produce a nitroanion radical that could react with oxygen to form a superoxide radical and affect the original nitroaromatic compound (Gonzalez-Perez et al. 2007; Nyanhongo et al. 2005).
Effects of several atypical antipsychotics closapine, sertindole or ziprasidone on hepatic antioxidant enzymes: Possible role in drug-induced liver dysfunction
Published in Journal of Toxicology and Environmental Health, Part A, 2021
Lena Platanić Arizanović, Aleksandra Nikolić-Kokić, Jelena Brkljačić, Nikola Tatalović, Marko Miler, Zorana Oreščanin-Dušić, Teodora Vidonja Uzelac, Milan Nikolić, Verica Milošević, Duško Blagojević, Snežana Spasić, Čedo Miljević
Ziprasidone exhibited the least noticeable effects on hepatic antioxidant enzymes, although ziprasidone is extensively metabolized in the liver principally via reduction by aldehyde oxidase. Approximately one-third of ziprasidone metabolic clearance is mediated by the cytochrome P-450 (CYP) 3A4 isoenzyme, the major CYP contributing to the oxidative metabolism of ziprasidone (American Society of Health-System Pharmacists 2015).