Structural Analysis of Amino Acids, Oxidized by Reactive Oxygen Species and an Antibody against N-Formylkynurenine

Abstract

Summary Amino acid oxidation, resulting from oxidative stress, is related to certain diseases and aging. To correlate reactive oxygen species with oxidized products of individual amino acids, we oxidized Met, Trp, His, and Tyr by treatment with singlet oxygen, superoxide, or hydroxyl radicals. The structures of oxidized amino acids were determined by nuclear magnetic resonance spectroscopy, infra-red spectroscopy, and fast atom bombardment-mass spectrometry. Among the compounds identified, N-formylkynurenine (NFK), a well-known oxidation product of Trp in vivo via enzymatic and non-enzymatic reactions, and its hydroxylated form were found to be major products of the reaction with singlet oxygen. Since NFK is a pivotal oxidation product of Trp, we raised antiserum against NFK by immunizing a rabbit with NFK-conjugated bovine serum albumin. The resulting antiserum was then used to detect photooxidized trypsin and kynurenine-conjuated ovalbumin as well as NFK-albumin. An antiserum such as this would be useful tool for detecting NFK and kynurenine in situ.