Interaction of reactive oxygen and nitrogen species with proteins

Free radicals and reactive oxygen or nitrogen species generated during oxidative stress and as by-products of normal cellular metabolism may damage all types of biological molecules. Proteins are major initial targets in cell. Reactions of a variety of free radicals and reactive oxygen and nitrogen species with proteins can lead to oxidative modifications of proteins such as protein hydroperoxides formation, hydroxylation of aromatic groups and aliphatic amino acid side chains, nitration of aromatic amino acid residues, oxidation of sulfhydryl groups, oxidation of methionine residues, conversion of some amino acid residues into carbonyl groups, cleavage of the polypeptide chain and formation of cross-linking bonds. Such modifications of proteins leading to loss of their function (enzymatic activity), accumulation and inhibition of their degradation have been observed in several human diseases, aging, cell differentiation and apoptosis. Formation of specific protein oxidation products may be used as biomarkers of oxidative stress.