DETECTION OF FREE-RADICALS PRODUCED FROM THE REACTION OF CYTOCHROME-P-450 WITH LINOLEIC-ACID HYDROPEROXIDE

The ESR spin-trapping technique was employed to investigate the reacti on of rabbit cytochrome P-450 1A2 (P450) with linoleic acid hydroperox ide. This system was compared with chemical systems where FeSO4 or FeC l3 was used in place of P450. The spin trap 5,5'-dimethyl-1-pyrroline N-oxide (DMPO) Was employed to detect and identify radical species. Th e DMPO adducts of hydroxyl, O-2(-.), peroxyl, methyl and acyl radicals were detected in the P450 system. The reaction did not require NADPH- cytochrome P-450 reductase or NADPH. The same DMPO-radical adducts wer e detected in the FeSO4 system. Only DMPO-(OH)-O-. radical adduct and carbon-centred radical adducts were detected in the FeCl3 system. Pero xyl radical production was completely O-2-dependent. We propose that p olyunsaturated fatty acids are initially reduced to form alkoxyl radic als, which then undergo intramolecular rearrangement to form epoxyalky l radicals. Each epoxyalkyl radical reacts with O-2, forming a peroxyl radical. Subsequent unimolecular decomposition of this peroxyl radica l eliminates O-2(-.) radical.