Effect of amino acids on X-ray-induced hydrogen peroxide and hydroxyl radical formation in water and 8-oxoguanine in DNA.

Generation of hydrogen peroxide and hydroxyl radicals in L-amino acid solutions in phosphate buffer, pH 7.4, under X-ray irradiation was determined by enhanced chemiluminescence in the luminol-p-iodophenol-peroxidase system and using the fluorescent probe coumarin-3-carboxylic acid, respectively. Amino acids are divided into three groups according to their effect on the hydrogen peroxide formation under irradiation: those decreasing yield of H2O2, having no effect, and increasing its yield. All studied amino acids at 1 mM concentration decrease the yield of hydroxyl radicals in solution under X-ray irradiation. However, the highest effect is observed in the order: Cys > His > Phe = Met = Trp > Tyr. At Cys, Tyr, and His concentrations close to physiological, the yield of hydroxyl radicals decreases significantly. Immunoenzyme analysis using monoclonal antibodies to 8-oxoguanine (8-oxo-7,8-dihydroguanine) was applied to study the effect of amino acids with the most pronounced antioxidant properties (Cys, Met, Tyr, Trp, Phe, His, Lys, Arg, Pro) on 8-oxoguanine formation in vitro under X-ray irradiation. It is shown that amino acids decrease the content of 8-oxoguanine in DNA. These amino acids within DNA-binding proteins may protect intracellular DNA against oxidative damage caused by formation of reactive oxygen species in conditions of moderate oxidative stress.