modified residue that can arise from different natural residues O-(L-isoglutamyl)-L-threonine (2S)-2-amino-5-([(1S,2R)-1-amino-1-carboxypropan-2-yl]oxy)-5-oxopentanoic acid (2S,3R)-2-amino-3-([(4S)-4-amino-4-carboxybutanoyl]oxy)-propanoic acid 230.09027099609375 230.220001220703125 5-(threon-O3-yl)glutamate A protein modification that effectively converts an L-threonine residue to O-(L-isoglutamyl)-L-threonine, using free L-glutamine and releasing ammonia, or using a peptidyl L-glutamine and releasing ammonia. C 9 H 14 N 2 O 5 MOD:01979 O(beta)-(gamma-glutamyl)threonine O-(L-isoglutamyl)-L-threonine O3-(isoglutamyl)threonine PSI-MOD T, X This is not an ester cross-link of peptides [JSG]. hypothetical crosslinked L-threonine residue