Cobaltous ion inhibition of lipid peroxidation in biological membranes.

The effect of cobalt on lipid peroxidation in biological membranes, phospholipid liposomes and fatty acid micelles was investigated. Cobaltous ion, at micromolar concentrations, inhibited iron-ascorbate induced lipid peroxidation in erythrocyte ghosts, microsomes and phosphatidylserine liposomes at pH 7.4. The pH seemed to be important for the anti-peroxidative effect of cobalt, because under slightly acidic conditions cobalt did not inhibit peroxidation. Cobalt was less effective in inhibiting peroxidation stimulated by organic hydroperoxides. Iron-ascorbate induced lipid peroxidation was also inhibited by EDTA. However, certain ratios of EDTA: cobalt in the reaction mixture stimulated peroxidation. Cobalt did not inhibit lipid peroxidation in linoleic acid micelles and phosphatidylethanolamine liposomes. The presence of phosphatidylserine, however, rendered these micelles and liposomes to cobalt inhibition. We conclude that the cobaltous ion is a potent inhibitor of lipid peroxidation in biological membranes and that the binding of cobalt to phosphatidylserine is necessary for the inhibitory effect of this metal ion.