Tryptophan: antioxidant or target of oxidative stress? A quantum chemistry elucidation

The Density Functional Theory was used to investigate oxidative stress related reactions of tryptophan in its free zwitterionic form. It was concluded that free tryptophan cannot be considered as an antioxidant, and that tryptophan residues in proteins are not especially good targets of oxidative stress. Its previously observed antioxidant abilities can then be attributed to tryptophan metabolites.