Free radical formation in the oxidation of malondialdehyde and acetylacetone by peroxidase enzymes.

Malondialdehyde, a product of lipid peroxidation, and acetylacetone undergo one-electron oxidation by peroxidase enzymes to form free radical metabolites, which were detected with ESR using the spin-trapping technique. The structures of the radical adducts were assigned using isotope substitution. With both malondialdehyde and acetylacetone and the enzymes myeloperoxidase and chloroperoxidase, carbon-centered radicals were detected. With horseradish peroxidase, a carbon-centered radical was initially trapped and then disappeared with the concomitant appearance of an iminoxyl radical.