Superoxide and nitric oxide are key elements of ROS and RNS, respectively, produced in cells under normal physiological conditions, and both species react with other molecules and also with each other to form a diverse array of additional ROS and RNS. Shey-Shing Sheu, in Cardiac Electrophysiology: From Cell to Bedside (Seventh Edition), 2018 Overview of Mitochondrial Reactive Oxygen Species Generation and Mitochondrial Membrane Potential Similarly, proteomic studies on two nitrogen fixing Anabaena strains exposed to U revealed the increased U tolerance in Anabaena strain L-31(LD 50 of 200 μM U) as compared to Anabaena strain PCC 7120 (LD 50 of 75 μM U) due to induction of oxidative stress-related proteins like MnSOD in L-31 as compared to PCC 7120 ( Panda, Basu, Acharya, Rajaram, & Apte, 2017). Proteomic profiling of Geobacter sulfurreducens displayed increased levels of oxidative stress-related genes including several efflux pumps belonging to the RND (resistance-nodulation-cell division) family, superoxide dismutase, and superoxide reductase ( Orellana et al., 2014). coli cells exposed to uranium ( Khemiri et al., 2014). Enhanced levels of SOD were also observed in E. In 50 μM uranium exposed cells, higher levels of SOD were observed compared to control cells of a marine yeast, Yarrowia lipolytica which facilitated the organism’s defense against uranium-induced oxidative stress ( Kolhe et al., 2020). MDPMK-02 isolated from toxic metal contaminated sites showed elevated levels of SOD and catalase upon arsenic and cadmium exposure ( David, Krishna, & Sangeetha, 2016). This is the first report for the enhancement of periplasmic SOD defense against external superoxide of environmental origin. Ver3, isolated from high altitude lake (> 4000 m) ( Schnell & Steinman, 1995). In the presence of extracellular superoxide, increased levels (~ 20-fold) of periplasmic CuZnSOD was observed in Acinetobacter sp. Similarly, in Thermus thermophilus HB27, induction of SOD protected the cells from mercury toxicity ( Norambuena, Hanson, Barkay, & Boyd, 2019). coli cells resulted into alleviation of ROS levels by SOD ( Ackerley, Barak, Lynch, Curtin, & Matin, 2006 Fathima & Rao, 2018). In bacteria, another type of SOD, i.e., nickel SOD (Ni-SOD) has also been reported with nickel as metal cofactor ( Youn, Kim, Roe, HAH, & KANG, 1996). Based on the metal cofactor requiring for its activity, SOD is classified into three major groups such as (i) Fe-SOD present in prokaryotes and chloroplasts of plants, (ii) Mn-SOD found in prokaryotes and mitochondria of eukaryotes, and (iii) Cu/Zn-SOD predominantly in eukaryotes and distributed in cytosol, chloroplasts, and peroxisomes ( Ighodaro & Akinloye, 2018). SOD is first-line defense mechanism in any organism that convert the dismutation of two molecules of superoxide radicals (O 2.) into molecular oxygen (O 2) and hydrogen peroxide (H 2O 2). Nilesh Kolhe, in Microbial and Natural Macromolecules, 2021 Superoxide dismutase The levels of superoxide are kept low by effective compartmentalization of the sequential reductions of oxygen and by extensive expressions of superoxide dismutases with high affinities for superoxide.Ĭelin Acharya. Evidence supports the expectation that superoxide is relatively unreactive toward most biological molecules, although the low levels of superoxide permitted in cells and tissues indicate that limiting cell exposures to superoxide is a significant selector for survival ( Fridovich 1983). In addition, superoxide does not cross lipid membranes readily. As a result, superoxide is generally a better reducing agent than oxidizing agent. A second reduction of superoxide would require the energetically disfavored compression of two full negative charges on a diatomic molecule. ), which exhibits a p K a of 4.8, meaning that the anion radical form is by far the predominant species at physiological pH ranges.In aqueous media, protonation of superoxide can form the uncharged hydroperoxyl radical (HOO Superoxide, which is an anion radical, is produced by the one-electron reduction of molecular oxygen. Smith, in Comprehensive Toxicology, 2010 1.14.4.1.1(i) Superoxide (O 2
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