Mitochondrial formation of hydrogen peroxide is causally linked to the antimycin A-mediated prevention of tert-butylhydroperoxide-induced U937 cell death.

Antimycin A and 2-heptyl-4-hydroxyquinoline N-oxide (HQNO), both of which bind to the same site of complex III, prevented U937 cell killing promoted by tert-butylhydroperoxide (tB-OOH). This cytoprotection was not directly caused by inhibition of electron transport or reduced formation of tB-OOH-derived toxic species, but rather appeared to be the consequence of a mechanism involving mitochondrial formation of hydrogen peroxide. Ubisemiquinone was most likely the electron donor allowing the formation of superoxides and, as a consequence, of hydrogen peroxide.