MECHANISM OF THE ANTIMYCIN A-MEDIATED ENHANCEMENT OF T-BUTYLHYDRAPEROXIDE-INDUCED SINGLE-STRAND BREAKAGE IN DNA

Inhibitors of complex III increased the DNA strand scission induced by t-butylhydroperoxide (tB-OOH) and cumene hydroperoxide but did not af fect DNA damage induced by H2O2. The hypothesis that these effects are selectively linked to inhibition of the electron transport from cytoc hrome b to cytochrome c(1) is validated by the following observations: (1) two complex III inhibitors, antimycin A and 2-heptyl-4-hydroxyqui noline N-oxide, enhanced the tB-OOH-induced DNA cleavage over the same concentration range as that in which inhibition of oxygen consumption was observed; (2) the complex III inhibitor-mediated enhancement of t B-OOH-induced DNA damage was abolished by the complex I inhibitor rote none or by glucose omission, and (3) the enhancing effects of antimyci n A were not observed in respiration-deficient cells. The mechanism wh ereby the complex III inhibitors potentiate DNA cleavage promoted by t B-OOH was subsequently investigated with intact as well as permeabiliz ed cells. H2O2, produced at the level of mitochondria via a Ca2+-depen dent process, was found to account for the enhancing effects of antimy cin A.