L-aspartic acid (His) -22.031969070434570312 -22.049999237060546875 115.02693939208984375 115.089996337890625 An artifactual protein modification that converts an L-histidine residue to L-aspartic acid by oxidative degradation. C -2 H -2 N -2 O 2 C 4 H 5 N 1 O 3 From OMSSA: desc="oxidation of H to D" monomass= -23.015984 (this is the same mass difference as OMSSA:54, his2asnh) [JSG]. H His->Asp MOD:00776 PSI-MOD Unimod:349 artifact his2asph histidine oxidation to aspartic acid modified L-histidine residue natural, standard, encoded residue substitution