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Selenium Remediation Using Granular and Biofilm Systems
Published in Y.V. Nancharaiah, Vayalam P. Venugopalan, Microbial Biofilms in Bioremediation and Wastewater Treatment, 2019
Lea C. Tan, Joyabrata Mal, Piet N.L. Lens
Reduction of Se-oxyanions is widespread in natural environments and is more likely that biotic mechanisms, such as assimilatory and dissimilatory selenium reduction (Figure 2), are responsible for the presence of selenide in the environment rather than abiotic reduction (Mal et al. 2016b, Nancharaiah and Lens 2015). Assimilatory reduction of Se-oxyanion is the uptake and reduction of selenate for the synthesis of selenomethionine and selenocysteine to be used in selenium-containing enzymes and compounds as cofactors in several enzymes. Assimilatory selenate reduction is generally used by both aerobes and anaerobes. More than 50 distinct selenoprotein families are currently known including glutathione peroxidase (GPx), thioredoxin reductase, tetraiodothyronine deiodinase, selenophosphate synthetase, and selenoprotein P (Labunskyy et al. 2014). Although their distribution varies greatly among species, they are present in all three domains of life. Other organic forms of Se, e.g., dimethyl selenide (DMSe) and dimethyl diselenide (DMDSe), result from bacterial methylation processes.
Se, 34]
Published in Alina Kabata-Pendias, Barbara Szteke, Trace Elements in Abiotic and Biotic Environments, 2015
Alina Kabata-Pendias, Barbara Szteke
A high proportion of Se (around 20% of the total production) is used as dietary supplement for humans and livestock. It is added, mainly as sodium selenite (Na2SeO3), to fertilizers, insecticides, and as supplement in the plant–animal–human food chain. Although small amounts of Se are considered beneficial, it can be hazardous in larger quantities. Trace Se amounts are necessary for cellular function in humans and animals. It is a component of the antioxidant enzymes glutathione peroxidase and thioredoxin reductase, and in three deiodinase enzymes is involved in thyroid hormones.
Arsenals of Pharmacotherapeutically Active Proteins and Peptides: Old Wine in a New Bottle
Published in Debarshi Kar Mahapatra, Swati Gokul Talele, Tatiana G. Volova, A. K. Haghi, Biologically Active Natural Products, 2020
Many proteins involved in redox reactions are selenoproteins [2]. For example, glutathione (GSH) reductases involved in the reduction of hydro-peroxides [2], thioredoxin reductase functioning in NADPH dependent reduction of thioredoxin, iodothyronine deiodinase in thyroid hormone formation, selenoprotein W in muscle metabolism, sperm capsule seleno-protein required for motility of sperms [3].
Association between polychlorinated biphenyl exposure and thyroid hormones: a systematic review and meta-analysis
Published in Journal of Environmental Science and Health, Part C, 2022
Christine C. Little, Joshua Barlow, Mathilda Alsen, Maaike van Gerwen
In addition to effects mediated by structural homology, PCBs are known to disrupt metabolism of thyroid hormones through alterations in the enzymatic processes of deiodination and glucuronidation. PCBs have been shown to upregulate T4 glucuronidation via induction of hepatic UDP-glucuronosyltransferase in rat models, thereby reducing levels of circulating T4.7,44 Additionally, PCBs may impact thyroid homeostasis by disrupting extrathyroidal conversion of T4 to T3. Conversion of T4 to its biologically active form T3 is tightly controlled by three types of deiodinases in human metabolism. Type-I and type-II deiodinases catalyze the removal of iodine residues from the outer ring of T4 to form T3, whereas type-III deiodinase catalyzes the removal of iodine from the inner ring of T4 or T3 to form the biologically inactive hormone reverse T3 (rT3).45 PCBs have been demonstrated to decrease activity of type-I and type-II deiodinases,7,45,46 while increasing activity of type-III deiodinase,47 though it is important to note that many of these effects appear to be tissue-dependent and vary between studies. Thus, PCB exposure may decrease circulating levels of T3 by impairing conversion of T4 into T3 and by promoting inactivation of T3 into rT3. In addition, PCBs have been shown to alter male and female reproductive hormones due to their estrogen-like structure.48–50 Reproductive hormones are known to directly influence thyroid hormone levels through regulation of the transport protein thyroxine binding globulin, providing an indirect pathway through which PCBs may disrupt thyroid hormone homeostasis.51–53