Experiments were performed which illustrate the various ways EDTA can influence lipid peroxidation. Either detergent-dispersed linoleate, or liposomes made from extracted microsomal phospholipids were utilized as substrates for peroxidation. Peroxidation was accomplished using Fe2+ or Fe3+. In systems utilizing Fe2+, EDTA chelation facilitated Fe2+ autoxidation which in turn caused peroxidation of detergent-dispersed linoleate. Peroxidation was not initiated during EDTA-Fe2+ autoxidation when the substrate lipids were in a liposomal configuration. Systems utilizing Fe3+ required an enzyme (either xanthine oxidase or NADPH-cytochrome P450 reductase) to reduce the iron for peroxidative activity. EDTA chelation of Fe3+ enhanced the xanthine oxidase and NADPH-cytochrome P450 reductase-catalyzed peroxidation of detergent-dispersed linoleate, presumably by facilitating the reduction of Fe3+. Catalase and mannitol inhibited both EDTA-Fe2+- and EDTA-Fe3+-dependent lipid peroxidation. EDTA-Fe3+ was not capable of initiating peroxidation of phospholipid liposomes following enzymatic reduction by either enzyme, but ADP-chelated iron effectively initiated liposomal peroxidation in similar systems. With xanthine oxidase-catalyzed peroxidation of liposomes with ADP-Fe3+, the inclusion of EDTA-Fe3+ caused a modest enhancement of activity. EDTA-Fe3+ greatly stimulated NADPH-cytochrome P450 reductase-catalyzed peroxidation of liposomes with ADP-Fe3+. In contrast, the addition of EDTA, rather than EDTA-Fe3+ inhibited the liposomal peroxidation catalyzed by either enzyme with ADP-Fe3+ when the EDTA concentration exceeded the concentration of Fe3+.
All Science Journal Classification (ASJC) codes
- Molecular Biology