Age pigments and free radicals: fluorescent lipid complexes formed by iron- and copper-containing proteins

Haem and non-haem iron-containing proteins stimulate lipid peroxidation with the formation of fluorescent lipid complexes. This process requires the presence of lipid hydroperoxides which release ferrozine-reactive iron from haem-containing proteins. Stimulation of lipid peroxidation by the released iron is inhibited by the iron chelator desferrioxamine. Copper ions, although more stimulatory towards fluorescent lipid complex formation than iron ions, do not stimulate lipid peroxidation when tightly bound at the active centre of proteins, but are reactive when loosely bound to albumin and histidine.