Table 2.

Summary of the main modes of mitochondrial ROS production. The dominate electron transport chain site is listed for each mode. The site may vary according the prevailing conditions. In practice, when one considers Table 1, other sites will also operate depending on the substrates being oxidized (e.g., pyruvate dehydrogenase (PDH) in mode 2). X denotes that a given variable has no known appreciable role in governing the mode.

Mode	OXPHOS	Respiration	Δp	NADH	QH2	Dominant ETC Site(s)
1	High	High	Mod	Low to mod	Low	Complex I (forward)
2	Low-mod	Low-mod	X	High	Intermediate	Complex I (forward), complex II
3	Low-mod	Low-mod	Mod	X	Intermediate	Complex III, complex II
4	Negligible	Some *	High	X	High	Complex I (reverse)

* Needs some for complex III and IV to keep Δp high.