Investigation into the Reactivity between Various Amino Acids and Oxygen-Derived Free Radicals by Use of the ESR Spin Trapping Method.

Abstract

Considerable attention has recently centered on the possible role of oxygen-derived free radicals in protein damage and degradation. In the present study, we investigated the reactivity of amino acids with superoxide and hydroxyl radical by an electron spin resonance assay using 5, 5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin trap. The intensity of the DMPO-OOH spin adduct generated from the hypoxanthine-xanthine oxidase system decreased in the presence of some amino acids such as cysteine and methionine at a final concentration of 1-10mM. However it was not influenced by the presence of other amino acids at the same final concentrations. The relative intensity of the DMPO-OH spin adduct generated from the Fenton reaction significantly decreased in the presence of various amino acids, especially aromatic amino acids, sulfur-containing amino acids, and histidine. The inhibition of DMPO-OH signal was not due to the inhibition of the Fenton reaction, but due to the competition of the amino acid with DMPO. In the early step of protein damage by active oxygen species, such amino acids residues are attacked.