iodoacetic acid derivatized residue modified L-tryptophan residue iodoacetic acid - site W 244.0847930908203125 244.25 58.0054779052734375 58.04000091552734375 C 13 H 12 N 2 O 3 C 2 H 2 O 2 Carboxymethyl Iodoacetic acid derivative MOD:01328 PSI-MOD There is no citation for this Unimod entry. Iodoacetic acid derivatization of tryptophan is not mentioned in the citation [JSG]. Unimod:6 W artifact modification from Unimod Chemical derivative - hydroxylethanone