title: Conversion of methionine into homocysteic acid in heavily oxidized proteomics samples.
abstract: Analysis of protein oxidation is necessary in numerous areas of biochemistry, including hydroxyl radical surface mapping, oxidative stress assays, and pharmaceutical stability testing. Mass spectrometry is one of the tools most often used to identify protein oxidation products, and previous studies have attempted to identify and characterize all of the major oxidation products detected by mass spectrometry for each amino acid residue. In this note, we present evidence that in heavily oxidized protein samples, such as those produced by hydroxyl radical surface mapping, a major oxidation product of methionine is homocysteic acid. The formation of homocysteic acid from methionine was previously unrecognized in other mass spectrometric analyses, and has important implications for the analysis of oxidized samples, as well as potential implications as to the functional consequences of methionine oxidation.
authors.affiliation: Palo Alto Research Center, 3333 Coyote Hill Rd., Palo Alto, CA 94304, USA. bern@parc.com
authors.forename: Marshall
authors.initials: M
authors.lastname: Bern
authors.forename: Jessica
authors.initials: J
authors.lastname: Saladino
authors.forename: Joshua S
authors.initials: JS
authors.lastname: Sharp
mesh_terms: D006710:Homocysteine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D008715:Methionine / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism; D040901:Proteomics / Q000379:methods*; D015203:Reproducibility of Results; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D010455:Peptides; D006710:Homocysteine; C007956:homocysteic acid; D008715:Methionine