isopeptide crosslinked residues crosslinked residues with loss of ammonia L-alanyl-L-isoaspartyl cyclopeptide -17.026548385620117188 -17.030000686645507812 169.061309814453125 169.160003662109375 CROSSLNK Alanine isoaspartyl cyclopeptide (Ala-Asn) Cross-link 2. H -3 N -1 (2S,5S)-2-methyl-3,7-dioxo-1,4-diazepane-5-carboxylic acid N-term A, N natural A protein modification that effectively converts an L-alaine residue and an L-asparagine residue to L-alanyl-L-isoaspartyl cyclopeptide. L-alanyl-L-isoaspartyl cyclopeptide C 7 H 9 N 2 O 3 MOD:01618 PSI-MOD 1,4.2-anhydro(L-alanyl-L-aspartic acid) crosslinked L-alanine residue crosslinked L-asparagine residue