modified residue that can arise from different natural residues glutamyl semialdehyde 113.04767608642578125 113.04767608642578125 113.1100006103515625 113.1100006103515625 none A protein modification that effectively converts a source amino acid residue to an L-glutamyl semialdehyde. C 5 H 7 N 1 O 2 X C 5 H 7 N 1 O 2 MOD:01440 artifact PSI-MOD L-glutamic gamma-semialdehyde (S)-2-amino-5-oxopentanoic acid