Table 1 Enzymatic antioxidants

From: Hydrogen peroxide: a Jekyll and Hyde signalling molecule

Enzymatic antioxidant

Cellular location

Substrate

Reaction

Superoxide dismutase (Mn/Cu/ZnSOD)

Mitochondrial matrix (MnSOD)

Cytosol (Cu/ZnSOD)

Superoxide (O2·−)

O2·− → H2O2

Catalase

Peroxisomes

Cytosol

Hydrogen peroxide (H2O2)

2H2O2 → O2+H2O

Glutathione peroxidase (GPX)

Cytosol

Hydrogen peroxide (H2O2)

H2O2+GSH → GSSG+H2O

Peroxiredoxin I → VI (Prx)

Cytosol

Hydrogen peroxide (H2O2)

H2O2+TrxS2 → Trx(SH)2+H2O

  1. Superoxide dismutases (SODs) catalyse the breakdown of superoxide into oxygen and H2O2. These enzymes, located in the cytosol and mitochondria, require a metal ion cofactor, copper (Cu), zinc (Zn) or manganese (Mn). Catalase is localised to the peroxisome, where it converts H2O2 to water and oxygen. Glutathione peroxidases are a large family of enzymes that reduce H2O2 to water. They are found both in the cytoplasm and extracellularly in almost every human tissue. Prxs catalyse the reduction of H2O2, organic hydroperoxides as well as peroxynitrite (ONOO−). Please note that several non-enzymatic antioxidants exist, including thioredoxin; vitamin A, C and E; and melatonin. The varied expression profiles, subcellular locations and substrates of the above mentioned antioxidant systems reflect the complex nature of ROS biology. It is clear that they are vital to escape oxidative damage and ensure cell survival
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