monohydroxylated residue modified glycine residue 2-hydroxyglycine observational artifact 15.994915008544921875 16.0 73.01638031005859375 73.0500030517578125 G MOD:01180 2HyGly artifact A protein modification that effectively converts a glycine residue to 2-hydroxyglycine. alpha-hydroxyglycine aminohydroxyacetic acid 2-hydroxyglycine PSI-MOD amino(hydroxy)acetic acid C 2 H 3 N 1 O 2 none O 1 CAUTION - peptides of 2-hydroxyglycine are known to be unstable, decaying to break the peptide backbone or to form peptidyl amides [see J. Am. Chem. Soc. 111, 1933-1934, 1989, and J. Org. Chem. 57, 3916-3921, 1992]. If computer analysis of tandem mass-spectrometric results predicts this modification, then it is most probable that there are multiple isobaric peptides differing in the location of multiple hydroxylation modifications [JSG].