2.02012-07-30 14:55:13 -06002015-06-03 17:21:05 -0600ECMDB21285M2MDB001691Superoxide anionThe superoxide ion, also known by the obsolete name hyperoxide, is a compound that contains the superoxide anion with the chemical formula O2-. The systematic name of the anion is dioxide. The superoxide anion is particularly important as the product of the one-electron reduction of dioxygen O2, which occurs widely in nature. With one unpaired electron, the superoxide ion is a free radical, and, like dioxygen, it is paramagnetic.; Because superoxide is toxic, nearly all organisms living in the presence of oxygen contain isoforms of the superoxide scavenging enzyme, superoxide dismutase, or SOD. SOD is an extremely efficient enzyme; it catalyzes the neutralization of superoxide nearly as fast as the two can diffuse together spontaneously in solution. Other proteins, which can be both oxidized and reduced by superoxide, have weak SOD-like activity (e.g. hemoglobin). Genetic inactivation ('knockout') of SOD produces deleterious phenotypes in organisms ranging from bacteria to mice and have provided important clues as to the mechanisms of toxicity of superoxide in vivo.; Superoxide is the anionic form O2. It is important as the product of the one-electron reduction of dioxygen (oxygen gas), which occurs widely in nature. With one unpaired electron, the superoxide ion is a free radical. It is also paramagnetic. The biological toxicity of superoxide is due to its capacity to inactivate iron-sulfur cluster containing enzymes (which are critical in a wide variety of metabolic pathways), thereby liberating free iron in the cell, which can undergo fenton-chemistry and generate the highly reactive hydroxyl radical. In its HO2 form, superoxide can also initiate lipid peroxidation of polyunsaturated fatty acids. It also reacts with carbonyl compounds and halogenated carbons to create toxic peroxy radicals. As such, superoxide is a main cause of oxidative stress.; Highly reactive compounds produced when oxygen is reduced by a single electron. In biological systems, they may be generated during the normal catalytic function of a number of enzymes and during the oxidation of hemoglobin to Methemoglobin.; Because superoxide is toxic, nearly all organisms living in the presence of oxygen contain isoforms of the superoxide scavenging enzyme, superoxide dismutase, or SOD. SOD is an extremely efficient enzyme; it catalyzes the neutralization of superoxide nearly as fast as the two can diffuse together spontaneously in solution. With one unpaired electron, the superoxide ion is a free radical and therefore paramagnetic.; In living organisms, superoxide dismutase protects the cell from the deleterious effects of superoxides.(O2)DioxidanidylDioxide(1)Dioxide(1-)HyperoxidHyperoxideO2O2 free radicalO2-O2.-O<SUB>2</SUB><SUP>-</SUP>Peroxide radicalSuperoxideSuperoxide anionSuperoxide anion radicalSuperoxide radicalSuperoxide radical anionSuperoxydeO231.998831.989829244oxidanidyloxidanylsuperoxide11062-77-4[O][O-]InChI=1S/HO2/c1-2/h1H/p-1OUUQCZGPVNCOIJ-UHFFFAOYSA-MSolidCytosolExtra-organismPeriplasmlogp-0.36pka_strongest_acidic5.8pka_strongest_basic-6.8iupacoxidanidyloxidanylaverage_mass31.9988mono_mass31.989829244smiles[O][O-]formulaO2inchiInChI=1S/HO2/c1-2/h1H/p-1inchikeyOUUQCZGPVNCOIJ-UHFFFAOYSA-Mpolar_surface_area23.06refractivity2.89polarizability1.67rotatable_bond_count0acceptor_count2donor_count0physiological_charge-1formal_charge-1Superoxide Radicals DegradationGram-negative bacteria commonly synthesize both cytoplasmic and periplasmic isozymes of SOD as their frontline defense against superoxide anion (O2-). E. coli contains two cytoplasmic SOD isozymes, one each of the manganese- and iron-cofactored types (MnSOD and FeSOD), and secretes a copper, zinc-cofactored enzyme (CuZnSOD) to the periplasm. Periplasmic superoxide may be generated by autooxidation of dihydromenaquinone in the cytoplasmic membrane.
In E. coli, the MnSOD and FeSOD enzymes (encoded by sodA and sodB, respectively) are structurally and kinetically similar. Unlike MnSOD and FeSOD, CuZnSOD is monomeric. Regulation of the three enzymes is complex. Under anaerobic conditions, FeSOD is the only superoxide dismutase enzyme present in E. coli. MnSOD is induced by aerobic growth and a variety of environmental stress conditions. CuZnSOD constitutes only a small fraction of superoxide dismutase activity in the cell; its expression is induced in stationary phase.
In E. coli, with rising H2O2 concentration, catalase is strongly induced and becomes the primary scavenging enzyme. E. coli expresses two catalases, known as HPI and HPII, that are encoded by katG and katE, respectively. While katG katE mutants could not degrade millimolar concentrations of H2O2, they were subsequently found to retain the ability to degrade H2O2 when it was present at low micromolar concentrations. This residual activity is due to an enzyme known as alkylhydroperoxide reductase (Ahp). This two-component enzyme had originally been identified as a scavenger of organic hydroperoxides.
SOD mutants of E. coli are unable to perform normal sulfur metabolism. Both SOD and catalase/peroxidase mutants of E. coli are incapable of synthesizing aromatic products, including amino acids.
SoxRS regulon is turned on by any condition that increases superoxide radical production in E. coli. One of its products is Mn-SOD. Another independent regulon turned on in response to H2O2 is referred to as the OxyR regulon. (EcoCyc)PW002053Metabolicsuperoxide radicals degradationDETOX1-PWYSpecdb::MsMs28355Specdb::MsMs28356Specdb::MsMs28357Specdb::MsMs34913Specdb::MsMs34914Specdb::MsMs34915Specdb::MsMs2562840Specdb::MsMs2562841Specdb::MsMs2562842HMDB0216853595974514331C0070418421SUPER-OXIDESuperoxide_anionKeseler, I. M., Collado-Vides, J., Santos-Zavaleta, A., Peralta-Gil, M., Gama-Castro, S., Muniz-Rascado, L., Bonavides-Martinez, C., Paley, S., Krummenacker, M., Altman, T., Kaipa, P., Spaulding, A., Pacheco, J., Latendresse, M., Fulcher, C., Sarker, M., Shearer, A. G., Mackie, A., Paulsen, I., Gunsalus, R. P., Karp, P. D. (2011). "EcoCyc: a comprehensive database of Escherichia coli biology." Nucleic Acids Res 39:D583-D590.21097882Superoxide dismutase [Mn]P00448SODM_ECOLIsodAhttp://ecmdb.ca/proteins/P00448.xmlProbable quinol monooxygenase ygiNP0ADU2YGIN_ECOLIygiNhttp://ecmdb.ca/proteins/P0ADU2.xmlSuperoxide dismutase [Cu-Zn]P0AGD1SODC_ECOLIsodChttp://ecmdb.ca/proteins/P0AGD1.xmlSuperoxide dismutase [Fe]P0AGD3SODF_ECOLIsodBhttp://ecmdb.ca/proteins/P0AGD3.xmlCatalase-peroxidaseP13029KATG_ECOLIkatGhttp://ecmdb.ca/proteins/P13029.xmlCatalase HPIIP21179CATE_ECOLIkatEhttp://ecmdb.ca/proteins/P21179.xmlOuter membrane protein NP77747OMPN_ECOLIompNhttp://ecmdb.ca/proteins/P77747.xmlOuter membrane pore protein EP02932PHOE_ECOLIphoEhttp://ecmdb.ca/proteins/P02932.xmlOuter membrane protein FP02931OMPF_ECOLIompFhttp://ecmdb.ca/proteins/P02931.xmlOuter membrane protein CP06996OMPC_ECOLIompChttp://ecmdb.ca/proteins/P06996.xml2 Hydrogen ion + 2 Superoxide anion > Hydrogen peroxide + OxygenSUPEROX-DISMUT-RXNMenaquinol 8 + 2 Oxygen >2 Hydrogen ion + Menaquinone 8 +2 Superoxide anion2 Oxygen + Ubiquinol-8 >2 Hydrogen ion +2 Superoxide anion + Ubiquinone-82 3-Hydroxyanthranilic acid + 4 Oxygen <> Cinnavalininate +2 Superoxide anion +2 Hydrogen peroxide +2 Hydrogen ionR02670Oxygen + Iron > Superoxide anion + Fe<SUP>3+</SUP>RXN-12541menadiol + Oxygen > Hydrogen ion + menadione + Superoxide anionRXN0-3441Hydrogen ion + Superoxide anion > Hydrogen peroxide + OxygenSUPEROX-DISMUT-RXN