Superoxide-dependent lipid peroxidation. Problems with the use of catalase as a specific probe for fenton-derived hydroxyl radicals

Hydroxyl radicals (OH·) can initiate lipid oxidation by hydrogen abstraction. Transition metals however, particularly iron and copper, stimulate lipid oxidation by reacting with lipid peroxides to form new radical species. The haem-iron protein catalase can react non-specifically with lipid peroxides in this way resulting in loss of their conjugated diene structures. When a superoxide-generating system is used to stimulate lipid autoxidation, catalase can conceivably inhibit the reaction in two ways (A) by decomposing lipid peroxides as they are formed (B) through the removal of hydrogen peroxide preventing OH· radical formation. Results presented here suggest that the latter interpretation, although commonly presented, cannot be automatically assumed.