Electron transfer facilitated by superoxide dismutase: a model for membrane redox systems?
Membranes, which are an amalgam of proteins and lipids, effect electron transfer through largely unknown mechanisms. Using albumin with bound fatty acids as a model, we have investigated the possible role of these two membrane constituents in electron transfer. In the presence of albumin: fatty acid, there is substantial enhancement of the reduction of ferricytochrome C by ferrous iron. To assess the possible role of free superoxide in cytochrome C reduction, we added mammalian copper/zinc containing superoxide dismutase (Cu/Zn SOD), which catalyzes the transfer of electrons between superoxide anion radicals, forming oxygen and hydrogen peroxide. Surprisingly, in the presence of either albumin or fatty acid free albumin, Cu/Zn SOD actually accelerates electron transfer from ferrous iron to ferricytochrome C. By contrast, neither inactive Cu/Zn SOD nor active manganese SOD facilitates the ferrous iron-dependent reduction of cytochrome C. These results suggest that, in some circumstances, Cu/Zn SOD may transfer electrons to alternative acceptors and that such transfer depends upon the unique reduction/oxidation reaction mechanism of Cu/Zn SOD. If so, this ubiquitous enzyme could be involved in regulating cellular electron transfer reactions as well as acting as a superoxide 'detoxify-ing' agent.
Peterson
D A
DA
Department of Medicine, V. A. Medical Center, Minneapolis, Minnesota.
Eaton
J W
JW
D000818:Animals; D002417:Cattle; D003574:Cytochrome c Group / Q000378:metabolism; D004050:Ditiocarb / Q000494:pharmacology; D004579:Electron Transport; D004912:Erythrocytes / Q000201:enzymology; D004926:Escherichia coli / Q000201:enzymology; D007700:Kinetics; D008566:Membranes / Q000378:metabolism; D008954:Models, Biological; D010084:Oxidation-Reduction; D012709:Serum Albumin / Q000494:pharmacology; D013482:Superoxide Dismutase / Q000378:metabolism*
D003574:Cytochrome c Group; D012709:Serum Albumin; D004050:Ditiocarb; D013482:Superoxide Dismutase