N-formylated residue modified L-tryptophan residue N-formyl-L-tryptophan 214.0742340087890625 214.220001220703125 27.994915008544921875 28.010000228881835938 C 12 H 10 N 2 O 2 A protein modification that effectively converts an L-tryptophan residue to N-formyl-L-tryptophan. From DeltaMass with no citation or formula: Average Mass: 214. It is not clear what this is supposed to represent. The mass corresponds to an N-formyl tryptophan (either N2 or N1'), but neither of these modifications has been reported as commonly encountered. It may have been confused with N'-formyl-L-kynurenine, see MOD:00464 [JSG] formyl tryptophanyl artifact C 1 O 1 PSI-MOD none W MOD:01106