title: Radiation chemical studies of methionine in aqueous solution: understanding the role of molecular oxygen.
abstract: The oxidation of methionine is an important reaction in the biological milieu. Despite a few decades of intense studies, several fundamental aspects remain to be defined. We have investigated in detail the gamma-radiolysis of free methionine in the absence and presence of molecular oxygen followed by product characterization and quantification. The primary site of attack by HO(*) radicals and H(*) atoms is the sulfur atom of methionine. We have disclosed that HO(*) radicals do not oxidize methionine to the corresponding sulfoxide in either the presence or the absence of oxygen; the oxidizing species is H(2)O(2) derived either from the radiolysis of water or from the disproportionation of the byproduct O(2)(*-). 3-Methylthiopropionaldehyde is the major product of HO(*) radical attack in the presence of molecular oxygen. Together with the direct oxidation at sulfur as the major product, the potential of H(*) atoms is also proven to be highly specific for sulfur atom attack under anoxic and aerobic conditions. The major products derived from the H(*) atoms attack are found to be alpha-aminobutyric acid or homoserine, in the absence or presence of oxygen, respectively. All together, these results help clarify the fate of methionine related to a biological environment and offer a molecular basis for envisaging other possible pathways of in vivo degradation as well as other markers.
authors.affiliation: ISOF, Consiglio Nazionale delle Ricerche, Via Piero Gobetti 101, 40129 Bologna, Italy.
authors.forename: Sebastián
authors.initials: S
authors.lastname: Barata-Vallejo
authors.forename: Carla
authors.initials: C
authors.lastname: Ferreri
authors.forename: Al
authors.initials: A
authors.lastname: Postigo
authors.forename: Chryssostomos
authors.initials: C
authors.lastname: Chatgilialoglu
mesh_terms: D002851:Chromatography, High Pressure Liquid; D005720:Gamma Rays; D017665:Hydroxyl Radical / Q000737:chemistry; D008715:Methionine / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D013481:Superoxides / Q000737:chemistry; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D013481:Superoxides; D017665:Hydroxyl Radical; D008715:Methionine; D010100:Oxygen