Protein-bound 3,4-dihydroxyphenylalanine is a major reductant formed during hydroxyl radical damage to proteins

Protein-bound dihydroxyphenylalanine (PB-DOPA) was generated by exposing proteins to hydroxyl radicals and enzymatically using mushroom tyrosinase. A comparison of DOPA levels in radical damaged or enzyme-treated proteins and those in cytochrome c reduction revealed that a large amount of reducing activity of the protein-bound reducing moiety originated from PB-DOPA. It was suggested that PB-DOPA might be involved in supplying reduced transition metal ions in free radical generating systems.