Mitochondrial Antioxidants and the Maintenance of Cellular Hydrogen Peroxide Levels

Table 1

Mitochondria can contain up to twelve sources of O₂^•−/H₂O₂. The twelve different enzymes are associated with nutrient metabolism and can be subcategorized in two groups: the NADH/NAD⁺ isopotential group and UQH₂/UQ isopotential group. The different sites make variable contributions to overall ROS release in different tissues.

Isopotential group	Enzyme	Site of production	High capacity site?
NADH/NAD^+	α-Ketoglutarate dehydrogenase	FAD (KF)	Yes: liver, muscle [8, 10]; No: cardiac [11]
	Pyruvate dehydrogenase	FAD (PF)	Yes: liver, muscle [8]; No: cardiac [11]
	Branched-chain keto acid dehydrogenase	FAD (BF)	Moderate: muscle [10]; Unknown: liver, cardiac.
	2-Oxoadipate dehydrogenase	FAD (OF)	Moderate: muscle [10]; Unknown: liver, heart
	Complex I	FMN (IF)	Yes: cardiac [11]; No: muscle, liver [8]
UQH2/UQ	Complex I	UQ binding site (IQ)	Yes: muscle [10]; Unknown: liver, cardiac
	Complex II	FAD (IIF)	Yes: muscle, liver (129 mice only), cardiac [61].; No: liver (C57Bl6N) [11].
	Complex III	UQ outer leaflet binding site (IIIQo)	Yes: muscle, liver, cardiac [8]
	Electron transfer flavoprotein: ubiquinone oxidoreductase	FAD (EF)	No: muscle [10]; Unknown: liver, cardiac
	sn-Glycerol-3-phosphate dehydrogenase	FAD (GF)	Yes: muscle, liver, cardiac [10]
	Proline dehydrogenase	FAD (PF)	No: muscle [10]; Unknown: liver, cardiac
	Dihydroorotate dehydrogenase	FAD (DF)	No: muscle [10]; Unknown: liver, cardiac