Amino acid peroxides, protein secondary

Tyramide signal amplification This procedure, designated as a catalyzed reporter deposition (CARD) or tyramide signal amplification (TSA), takes advantage of horseradish peroxidase (HRP) from an HRP-labeled secondary antibody to catalyze in the presence of hydrogen peroxide the oxidation of the phenol moiety of labeled tyramine. On oxidation by HRP, activated tyramine molecules rapidly bind covalently to electron-rich amino acids of proteins immediately surrounding the site of the immunoreaction. This allows an increase in the detection of an antigenic site up to 100-fold compared with the conventional indirect method with no loss in resolution. 

Among protein oxidation products, formation of protein peroxides should be mentioned. Protein peroxidation occurs as a reaction secondary to free-radical attack on amino acid side groups, effecting a carbon-centered free radical of amino acid formation. Such a radical reacts with the oxygen molecule and produces a hydroperoxide radical ... 

Oxidative amino acid side-chain modifications do not result in a stable end product of the oxidation process, but very often highly reactive intermediates are formed. These include chemically reactive groups, like ketones and aldehydes, or the formation of protein hydroperoxides. The presence of such protein hydroperoxides leads to a process called protein peroxidation. Here secondary reactions occur if the protein hydroperoxide decomposes and initiates further oxidative reactions, again forming oxidized protein forms. 

---