derives from trimethylated residue alpha-amino methylated residue alpha-amino trimethylated residue 1+ 42.0464019775390625 42.0800018310546875 A protein modification that effectively replaces an alpha-aminium group with a trimethylaminium group. C 3 H 6 N 0 O 0 For amino acids residues, amine trimethylation can effectively only be accomplished with an aminium, protonated primary amino, group. This process accounts only for trimethylation and not protonation. The alternative N2Me3+Res process (MOD:01698) accounts for both protonation and trimethylation. MOD:01687 N-term N2Me3Res PSI-MOD Trimethyl Unimod:37 X natural ntermtrimethyl tri-Methylation alpha-amino protonated residue