This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Synonyms: removal of superoxide radicals
|Superclasses:||Detoxification → Reactive Oxygen Species Degradation|
All organisms living in an aerobic environment are exposed to reactive oxygen species (ROS) that are formed through metabolic processes and various environmental stresses such as drought, air pollutants, UV light and high light intensities, chilling temperatures and external chemicals [Van99a, Alscher02]. For example, active oxygen species are produced during the β-oxidation of fatty acids or as a result of photorespiration in photosynthetic organisms [Frugoli96]. ROS such as superoxide and hydroxyl radicals as well as hydrogen peroxide can cause significant damage to proteins, nucleic acids and cell organelles.
Most of the aerobic organisms have developed defense systems to face oxidative stress and to scavenge oxidative radicals in the form of enzymes that can detoxify ROS, such as superoxide dismutase (SOD) and hydroperoxidase (CAT) [Beyer87]. For example, Arabidopsis thaliana, a member of the mustard family (oilseed plants), stores energy reserves preliminary as lipids that undergo β-oxidation during germination. The hydrogen peroxide that is produced during this metabolic process is detoxified by catalase. Another form of ROS, superoxide radicals, are by-products of aerobic electron transfer chains, and are disposed of by the action of superoxide dismutase. Since ROS can be found in any compartment of the eukaryotic cell, organisms have developed small gene families encoding for several SOD and CAT enzymes that operate in the various cell compartments [Kliebenstein98, McClung97].
About This Pathway
SODs represent the first line of defense against ROS, converting superoxide radicals to hydrogen peroxide and water. SODs are differentiated with regard to their metal cofactor. There are iron-dependent, manganese-dependent and copper/zinc-dependent SODs, which differ not only in their metal cofactor but also in their subcellular location. In plants, FeSODs are located in chloroplasts and are regarded the most ancient SOD group. MnSODs are found in the mitochondrion and the peroxisome and are structurally very similar to FeSODs. The last group, the Cu-ZnSODs operates in chloroplasts, the cytosol and even the extracellular space. They are structurally very different from the other two SOD groups because of the different electrical properties of copper in comparison to iron or manganese, which resulted in a major structural change in the protein [Alscher02].
To date seven SODs have been identified in Arabidopsis thaliana, three of them iron-dependent, three having copper as metal cofactor and one manganese-dependent SOD [Hindges92, Van90a, Kliebenstein98]. It has been demonstrated that a copper-chaperone (AtCCS, At1g12520) is crucial for the activation of all three Cu/Zn-dependent SODs in this organism. The SOD holoenzyme usually constitutes either a homodimer or a homotetramer. However, the exact composition of the SODs in Arabidopsis is currently not known and remains to be verified (here displayed as polypeptides).
Catalase is second in the defense line against active oxygen, converting hydrogen peroxide into water and oxygen. Three genes encoding subunits of catalase and at least 6 catalase isoenzymes have been identified in Arabidopsis so far [Zhong94, McClung97, Frugoli96, Zhong96]. Besides their implication in detoxifying ROS, catalases are thought to play a role in the signal transduction pathway in plants leading to the development of SAR (systemic aquired resistance) [Jones94c]. The functional protein of catalase is a tetramer but the question whether it exists as homo- or heterotetramer of different subunits remains to be investigated.
Chu05: Chu CC, Lee WC, Guo WY, Pan SM, Chen LJ, Li HM, Jinn TL (2005). "A copper chaperone for superoxide dismutase that confers three types of copper/zinc superoxide dismutase activity in Arabidopsis." Plant Physiol 139(1);425-36. PMID: 16126858
Frugoli96: Frugoli JA, Zhong HH, Nuccio ML, McCourt P, McPeek MA, Thomas TL, McClung CR (1996). "Catalase is encoded by a multigene family in Arabidopsis thaliana (L.) Heynh." Plant Physiol 112(1);327-36. PMID: 8819328
Hindges92: Hindges R, Slusarenko A (1992). "cDNA and derived amino acid sequence of a cytosolic Cu,Zn superoxide dismutase from Arabidopsis thaliana (L.) Heyhn." Plant Mol Biol 18(1);123-5. PMID: 1731963
Kliebenstein98: Kliebenstein DJ, Monde RA, Last RL (1998). "Superoxide dismutase in Arabidopsis: an eclectic enzyme family with disparate regulation and protein localization." Plant Physiol 118(2);637-50. PMID: 9765550
Van90a: Van Camp W, Bowler C, Villarroel R, Tsang EW, Van Montagu M, Inze D (1990). "Characterization of iron superoxide dismutase cDNAs from plants obtained by genetic complementation in Escherichia coli." Proc Natl Acad Sci U S A 87(24);9903-7. PMID: 2263641
Van99a: Van Breusegem F, Slooten L, Stassart J-M, Botterman J, Moens T, Van Montagu M, Inze D (1999). "Effects of overproduction of tobacco MnSOD in maize chloroplasts on foliar tolerance to cold and oxidative stress." Journal of Experimental Botany, 50(330), 71-78.
Zhong94: Zhong HH, Young JC, Pease EA, Hangarter RP, McClung CR (1994). "Interactions between Light and the Circadian Clock in the Regulation of CAT2 Expression in Arabidopsis." Plant Physiol 104(3);889-898. PMID: 12232134
Argaman12: Argaman L, Elgrably-Weiss M, Hershko T, Vogel J, Altuvia S (2012). "RelA protein stimulates the activity of RyhB small RNA by acting on RNA-binding protein Hfq." Proc Natl Acad Sci U S A 109(12);4621-6. PMID: 22393021
Battistoni95: Battistoni A, Rotilio G (1995). "Isolation of an active and heat-stable monomeric form of Cu,Zn superoxide dismutase from the periplasmic space of Escherichia coli." FEBS Lett 374(2);199-202. PMID: 7589534
Battistoni96: Battistoni A, Folcarelli S, Gabbianelli R, Capo C, Rotilio G (1996). "The Cu,Zn superoxide dismutase from Escherichia coli retains monomeric structure at high protein concentration. Evidence for altered subunit interaction in all the bacteriocupreins." Biochem J 320 ( Pt 3);713-6. PMID: 9003353
Battistoni98: Battistoni A, Donnarumma G, Greco R, Valenti P, Rotilio G (1998). "Overexpression of a hydrogen peroxide-resistant periplasmic Cu,Zn superoxide dismutase protects Escherichia coli from macrophage killing." Biochem Biophys Res Commun 243(3);804-7. PMID: 9501009
Beaumont93: Beaumont MD, Hassan HM (1993). "Characterization of regulatory mutations causing anaerobic derepression of the sodA gene in Escherichia coli K12: cooperation between cis- and trans-acting regulatory loci." J Gen Microbiol 139(11);2677-84. PMID: 8277251
Bebien02a: Bebien M, Lagniel G, Garin J, Touati D, Vermeglio A, Labarre J (2002). "Involvement of superoxide dismutases in the response of Escherichia coli to selenium oxides." J Bacteriol 184(6);1556-64. PMID: 11872706
Belkin96: Belkin S, Smulski DR, Vollmer AC, Van Dyk TK, LaRossa RA (1996). "Oxidative stress detection with Escherichia coli harboring a katG'::lux fusion." Appl Environ Microbiol 62(7);2252-6. PMID: 8779563
Benov95a: Benov L, Fridovich I (1995). "A superoxide dismutase mimic protects sodA sodB Escherichia coli against aerobic heating and stationary-phase death." Arch Biochem Biophys 322(1);291-4. PMID: 7574689
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