N'-formyl-L-kynurenine 218.0691375732421875 218.2100067138671875 31.989828109741210938 32.0 A protein modification that effectively converts an L-tryptophan residue to N'-formyl-L-kynurenine. C 11 H 10 N 2 O 3 Dioxidation Double oxidation of Trp From DeltaMass: References:Willy V. Bienvenut, Catherine Déon, Carla Pasquarello, Jennifer M. Campbell, Jean-Charles Sanchez, Marvin L. Vestal, Denis F. Hochstrasser Matrix-assisted laser desorption/ionization-tandemmass spectrometry with high resolution andsensitivity for identification and characterizationof proteins. Proteomics 2002, 2, 868-876 Notes: A double oxidation of tryptophan for which the N-formylkynurenine (+32) structure can be proposed. Many minor peaks accompanying the main peak might also be attributed to other oxidation products of the tryptophan such as kynurenine (+4), an unknown by-product found in all oxidized tryptophan patterns (+13), hydroxytryptophan (+16), 3-hydroxykynurenine (+20) and hydroxy-N-formylkynurenine (+48). See proposed structures at http://www.abrf.org/images/misc/dmass32.jpg. MOD:00464 O 2 PSI-MOD Unimod:425 W artifact dihydroxy formylkynureninw tryptophan oxidation to formylkynurenin carbon oxygenated residue modified L-tryptophan residue