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| Antioxidant enzyme | Cofactor/substrate | Reaction catalyzed | Location | Biochemical function |
|
| Copper-zinc-SOD (Cu, Zn-SOD, or SOD1) [93] | Copper and zinc | + + 2H+ → H2O2 | Cytosol, nucleus, mitochondria (intermembrane space) | Catalyzes the dismutation reaction of superoxide to H2O2 to decrease its reduction potential |
|
| Manganese SOD (MnSOD or SOD2) [93] | Manganese | + + 2H+ → H2O2 | Mitochondrial matrix | Same as above |
|
| Extracellular SOD (ecSOD or SOD3) [93] | Copper and zinc | + + 2H+ → H2O2 | Isoform secreted extracellularly | Same as above |
|
| Glutathione peroxidase (GPx) [93] | GSH
Selenium | () R-Se−H+ + ROOH/ONOO− → ROH/ONO− + R-SeOH
( ) 2GSH + R-SeOH → GS-SG + R-Se−H+ | Throughout the body | Reduce lipid hydroperoxides to alcohols and H2O2 to water |
|
| Glutathione-S-transferase (GST) [94] | GSH | GSH + RX → GSR + HX
X = leaving group
R = electrophilic group | Cytosol, mitochondria, peroxisome | Detoxification of xenobiotics |
|
| Glutathione reductase (GR) [94] | FAD
NADPH
GS-SG | GSSG + NADPH → 2GSH + NADP+ | Cytosol, mitochondrial matrix | Maintenance of GSH levels |
|
| Catalase (CAT) [93] | Fe2+ and | H2O2 → H2O + O2 | Throughout the body; lowest in the brain | Reduces H2O2 to water and oxygen |
|
| Peroxiredoxins (Prx) [95] | Thioredoxin (Trx) | () Prxred + H2O2 → Prxox + 2H2O
() Prxox + Trxred → Prxred + Trxox | Throughout the body (intracellular) | Reduces H2O2 to water
Prx is reduced by Trx to be used in subsequent reactions |
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