Hydrogen abstraction amino acids with peroxidized

In biological systems, free radicals can react with cellular macromolecules in a variety of ways, the most important of which is hydrogen abstraction from DNA leading to chain scission or cross-linking. In proteins, tryptophan is the amino acid residue most susceptible to free radical attack. Lipid peroxidation by free radicals in turn is liable to cause alteration in cell membranes. 

It should also be emphasized that benzyl radicals can be formed from toluene by hydrogen atom abstraction reactions. This may involve, for example, reaction with reactive oxygen-centered radicals derived from the photolysis of peroxides (see Amino Acids and Peptides later in this chapter). 

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