Table 2.

Cellular sources of ROS

Source	Cellular compartment	Primary radical generated
Complex IF	Mitochondria	${\mathrm{O}}_{2^{-}}$
Complex IQ	Mitochondria	${\mathrm{O}}_{2^{-}}$
Complex IIF	Mitochondria	${\mathrm{O}}_{2^{-}}$
Complex IIQ0	Mitochondria	${\mathrm{O}}_{2^{-}}$
mGPDH	Mitochondria	${\mathrm{O}}_{2^{-}}$
ETFQOR	Mitochondria	${\mathrm{O}}_{2^{-}}$
PDH	Mitochondria	${\mathrm{O}}_{2^{-}}$
OGDH	Mitochondria	${\mathrm{O}}_{2^{-}}$
BCKDH	Mitochondria	${\mathrm{O}}_{2^{-}}$
P66shc	Mitochondria, cytoplasm	H2O2
NOS	Cytoplasm	NO
NOX family	Cytoplasm, cell membrane	${\mathrm{O}}_{2^{-}}$
Xantine oxidase	Cytoplasm, peroxisome	H2O2
Cytochrome p450 family	Endoplasmic reticulum	${\mathrm{O}}_{2^{-}}$ H2O2

CI _F complex I flavin site, CI _Q complex I ubiquinone site, CII _F complex II flavin site and CIII _Q0 complex III_Qo are sites of the mitochondrial ETC, mGPDH Mitochondrial glycerol 3-phosphate dehydrogenase, ETFQOR electron-trasferring flavoprotein ubiquinone oxidoreductase, PDH pyruvate dehydrogenase, OGDH 2-oxoglutarate dehydrogenase and BCKDH branched-chain 2-oxoacid dehydrogenase are mitochondrial enzymes capable of generate ROS. Upon stress signaling, cytosolic p66Shc translocates to mitochondria to directly stimulate hydrogen peroxide generation. Nitric oxide synthase (NOS) produces NO^.by facilitating the conversion of l-arginine to l-citruline. NADPH oxidase family of enzymes (NOX) transfer electrons from NADPH to O₂ to produce O₂ ⁻. Other cellular enzymes incuding xanthine oxidase and cytochrome p450 families also participate in ROS generation in normal biological reactions and in chemicals or xenobiotics detoxification reactions