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.