Table 1.

Mitochondrial antioxidant defense system

Antioxidant system	Function	Significance	Ref
Enzymes
MnSOD	Facilitate dismutation of superoxide to H2O2	Efficient solely dependent on its own activity not any cofactor	84
Catalase	Detoxify H2O2	Less powerful than GSH	85
TrxR	Reduce Trx2 to Prx by utilizing NADPH	Similar to GR in GSH	26
Prx	Reduce H2O2 to oxygen using reducing equivalent from Trx	Similar to GPx in GSH system	86
γ-GST	Detoxify lipid peroxidation by consumption of GSH	Dependent on GSH availability	87
GR	Regenerate GSH utilizing NADPH	Catalyze the reaction to regenerate GSH	88
GPx
GPx1	Cytosolic GPx, Reduce H2O2 to H2O by utilizing GSH	Protect cells from acute oxidative stress	89, 90
GPx2	Gastrointestinal GPx, is upregulated in cancer cells and also a target of Nrf2	Part of adaptive response to cancer	91
GPx3
GPx4	Reduce phospholipids hydroperoxides, H2O2, cholesterol peroxides	Interfere with NF-κB, reduces leukotriene and prostanoid biosynthesis, prevent COX-2 expression	92
GPx6	Restrict to olfactory system		30
Small molecules
Trx2	Reduce H2O2 and lipid hydroperoxides	A supplement to GSH system	93
TP	Remove membrane lipid peroxide, and could be regenerated by CoQ or AA	It is the perimeter layer of ROS defense for mitochondrial	94
Glutathione	Detoxify H2O2, uptake from cytosol or regenerated by GR	Most important intracellular antioxidant	95
NADPH	Protect against oxygen centered radicals	Acting in accordance with other antioxidant network	96
Cytochrome c	Removal of superoxide	Contribute to generation of ATP	97

MnSOD: Manganese superoxide dismutase; TrxR: Thioredoxin reductase; γ-Glutathione-s transferase; Prx: Peroxiredoxin; GSH: glutathione; GR: glutathione reductase; GPx: glutathione peroxidase; Trx: Thioredoxin; TP: a-tocopherol ; NADPH: Nicotinamide Adenine Dinucleotide Phosphate