Stimulation of microsomal lipid peroxidation by iron and cysteine. Characterization and the role of free radicals

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Abstract
The stimulation of microsomal lipid peroxidation by FeSO4 and cysteine was investigated. Although both FeSO4 and cysteine alone promoted an increase in malonaldehyde production, when these agents were added together to [rat liver] microsomes the resultant level of malonaldehyde was greater than the sum of the amounts formed by these pro-oxidants when acting individually. A further indication of an interaction between FeSO4 and cysteine was shown by the inhibitory action of chelating agents. Stimulation of peroxidation was independent of microsomal protein, including cytochrome P-450. The system was characterized for the effects of cysteine, Fe2+ and O2 concentrations, pH, temperature and antioxidants. The high level of peroxidation attained with this system, its nonenzymic character and the involvement of hydroxyl radicals make it particularly useful for the investigation of the action of antioxidants. Furthermore, it may also be a model of the way in which decompartmentalized, delocalized or ''free'' Fe initiates peroxidation in vivo.