iodoacetic acid derivatized residue modified L-cysteine residue S-carboxymethyl-L-cysteine 161.0146636962890625 161.17999267578125 58.0054779052734375 58.04000091552734375 MOD:01061 C 5 H 7 N 1 O 3 S 1 carboxymethylc C Iodoacetic acid derivative Carboxymethyl none artifact A protein modification that effectively converts an L-cysteine residue to S-carboxymethyl-L-cysteine. Carboxymethyl cysteine PSI-MOD From DeltaMass with no citation, name misspelled "Carboxymethyl Cystenyl", and formula incorrect, N and O reversed: Average Mass: 161 Abbreviation: -Cmc- Formula: C5H7O1N3S1 Monoisotopic Mass Change: 161.015 Average Mass Change: 161.179 [JSG]. CmC C 2 H 2 O 2 Carboxymethyl Cystenyl