TERT-BUTYL HYDROPEROXIDE-INDUCED RADICAL PRODUCTION IN RAT-LIVER MITOCHONDRIA

When rat liver mitochondria are treated with tert-butyl hydroperoxide (TBHP) in the presence of the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO), electron paramagnetic resonance (EPR) signals are detected attributable to spin adducts resulting from the trapping of methyl, tert-butoxyl, and tert-butylperoxyl radicals. The addition of respiratory substrate results in a 3- to 7.5-fold increase in the signal intensity of the DMPO/methyl adduct, no change in the signal intensity of the DMPO/tert-butoxyl adduct, and complete loss of the DMPO/tert-butylperoxyl adduct signal. The magnitude of increase of methyl radical production in the presence of respiratory substrate is related to the respiratory control ratio (RCR) of the mitochondrial preparation. In the presence of antimycin A, which blocks electron flow between cytochromes b and c1, no stimulation of methyl radical production is detected with respiratory substrate. Stimulation of methyl radical production by the addition of respiratory substrate is detected in cytochrome c-depleted mitochondria. A similar increase in methyl radical production is detected when ferrous cytochrome is treated with TBHP in the presence of DMPO (as compared to when ferricytochrome c is used). These results indicate that TBHP is reduced directly by either cytochrome c1, cytochrome c, or by both of these electron transport chain components in mitochondria undergoing state 4 respiration.