Types Superoxide dismutase

1 types

1.1 general
1.2 human
1.3 plants
1.4 bacteria

types
general

irwin fridovich , joe mccord @ duke university discovered enzymatic activity of superoxide dismutase in 1968. sods known group of metalloproteins unknown function; example, cuznsod known erythrocuprein (or hemocuprein, or cytocuprein) or veterinary anti-inflammatory drug orgotein . likewise, brewer (1967) identified protein later became known superoxide dismutase indophenol oxidase protein analysis of starch gels using phenazine-tetrazolium technique.

there 3 major families of superoxide dismutase, depending on protein fold , metal cofactor: cu/zn type (which binds both copper , zinc), fe , mn types (which bind either iron or manganese), , ni type (which binds nickel).

copper , zinc – commonly used eukaryotes, including humans. cytosols of virtually eukaryotic cells contain sod enzyme copper , zinc (cu-zn-sod). example, cu-zn-sod available commercially purified bovine red blood cells. bovine cu-zn enzyme homodimer of molecular weight 32,500. first sod atomic-detail crystal structure solved, in 1975. 8-stranded greek key beta-barrel, active site held between barrel , 2 surface loops. 2 subunits tightly joined back-to-back, hydrophobic , electrostatic interactions. ligands of copper , zinc 6 histidine , 1 aspartate side-chains; 1 histidine bound between 2 metals.
iron or manganese – used prokaryotes , protists, , in mitochondria , chloroplasts

iron – many bacteria contain form of enzyme iron (fe-sod); bacteria contain fe-sod, others mn-sod, , (such e. coli) contain both. fe-sod can found in chloroplasts of plants. 3d structures of homologous mn , fe superoxide dismutases have same arrangement of alpha-helices, , active sites contain same type , arrangement of amino acid side-chains. dimers, tetramers.
manganese – mitochondria, , many bacteria, contain form manganese (mn-sod): example, mn-sod found in human mitochondria. ligands of manganese ions 3 histidine side-chains, aspartate side-chain , water molecule or hydroxy ligand, depending on mn oxidation state (respectively ii , iii).


nickel – prokaryotic. has hexameric (6-copy) structure built right-handed 4-helix bundles, each containing n-terminal hooks chelate ni ion. ni-hook contains motif his-cys-x-x-pro-cys-gly-x-tyr; provides of interactions critical metal binding , catalysis , is, therefore, diagnostic of nisods.

in higher plants, sod isozymes have been localized in different cell compartments. mn-sod present in mitochondria , peroxisomes. fe-sod has been found in chloroplasts has been detected in peroxisomes, , cuzn-sod has been localized in cytosol, chloroplasts, peroxisomes, , apoplast.

human

three forms of superoxide dismutase present in humans, in other mammals, , chordates. sod1 located in cytoplasm, sod2 in mitochondria, , sod3 extracellular. first dimer (consists of 2 units), whereas others tetramers (four subunits). sod1 , sod3 contain copper , zinc, whereas sod2, mitochondrial enzyme, has manganese in reactive centre. genes located on chromosomes 21, 6, , 4, respectively (21q22.1, 6q25.3 , 4p15.3-p15.1).

plants

in higher plants, superoxide dismutase enzymes (sods) act antioxidants , protect cellular components being oxidized reactive oxygen species (ros). ros can form result of drought, injury, herbicides , pesticides, ozone, plant metabolic activity, nutrient deficiencies, photoinhibition, temperature above , below ground, toxic metals, , uv or gamma rays. specific, molecular o2 reduced o2 (a ros called superoxide) when absorbs excited electron released compounds of electron transport chain. superoxide known denature enzymes, oxidize lipids, , fragment dna. sods catalyze production of o2 , h2o2 superoxide (o2), results in less harmful reactants.

when acclimating increased levels of oxidative stress, sod concentrations typically increase degree of stress conditions. compartmentalization of different forms of sod throughout plant makes them counteract stress effectively. there 3 well-known , -studied classes of sod metallic coenzymes exist in plants. first, fe sods consist of 2 species, 1 homodimer (containing 1-2 g fe) , 1 tetramer (containing 2-4 g fe). thought ancient sod metalloenzymes , found within both prokaryotes , eukaryotes. fe sods abundantly localized inside plant chloroplasts, indigenous. second, mn sods consist of homodimer , homotetramer species each containing single mn(iii) atom per subunit. found predominantly in mitochondrion , peroxisomes. third, cu-zn sods have electrical properties different of other 2 classes. these concentrated in chloroplast, cytosol, , in cases extracellular space. note cu-zn sods provide less protection fe sods when localized in chloroplast.

bacteria

human white blood cells use enzymes such nadph oxidase generate superoxide , other reactive oxygen species kill bacteria. during infection, bacteria (e.g., burkholderia pseudomallei) therefore produce superoxide dismutase protect being killed.