ROS Generation and Antioxidant Defense Systems in Normal and Malignant Cells

Table 1

ROS and major mechanisms of their generation and detoxification.

ROS	Generation	Detoxification
Superoxide radical (O2^•−)	Mitochondrial respiratory chain; Electron transport chain in the peroxisomal membrane; Superoxide dismutases; CYP catalytic cycle; Mitochondrial enzymes (glycerol 3-phosphate dehydrogenase, 2-oxoglutarate dehydrogenase, NADH-cytochrome b5 reductase, etc.); Xanthine oxidoreductase	Superoxide dismutases; Polyamines
Hydrogen peroxide (H2O2)	Spontaneous dismutation of superoxide radicals; Polyamine catabolism; Thymidine catabolism; NADPH oxidases; Monoamine oxidases; Lysyl oxidases; Dihydroorotate dehydrogenase; CYP catalytic cycle; Peroxisomal enzymes (acyl-CoA oxidases, d-amino acid oxidase, d-aspartate oxidase, etc.); Microsomal monooxygenase (MMO) system; Normal protein folding/unfolded protein response; Polyunsaturated fatty acid metabolism	Polyamines; Glutathione peroxidases; Thioredoxin peroxidases; Catalase; Peroxiredoxins; Glutathione S-transferases; Glutaredoxins; Thioredoxins; Nonenzymatic scavengers; Glycolysis; Pentose phosphate pathway
Hydroxyl radical (^•OH)	Fenton and Haber-Weiss reactions; Thymidine catabolism (supposed); Aconitase via Fenton reaction	^•OH has a very short half-life and is very rapidly involved in other reactions; Polyamines
Singlet oxygen (O2)	Nonphotosensitized mechanisms of O2 generation	O2 is rapidly implicated in many oxidation reactions; Polyamines
Hydroperoxyl radical (HOO^•)	Protonated form of O2^•−	Nonenzymatic scavengers
Peroxyl radical (ROO^•)	Polyunsaturated fatty acid metabolism	Nonenzymatic scavengers
Alkoxyl radical (RO^•)	Polyunsaturated fatty acid metabolism	Nonenzymatic scavengers

Described in [150, 269]; well reviewed in [270].