Table 1.

Endogenous antioxidant defense.

Enzymatic Antioxidants	Mechanism
Superoxide dismutase	Metal-containing proteins that catalyze the dismutation of superoxides to hydrogen peroxide [39].
Catalase	Catalyze hydrogen peroxide to water and molecular oxygen [39].
Glutathione peroxidase (GPx)	Selenocysteine-containing residues at its active site to catalyze hydrogen peroxide to water and lipid peroxides to corresponding alcohols [58].
Glutathione reductase (GR)	Catalyze the reduction of GSSG to GSH [71].
Glutathione S-transferase (GST)	Catalyze the conjugation of the GSH to hydrophobic substrates that decrease toxicity and are predisposed to elimination from cells [72].

GSH, reduced from glutathione; GSSG, oxidized from glutathione.