Distinguishing Aspartic and Isoaspartic Acids in Peptides by Several Mass Spectrometric Fragmentation Methods.
Six ion fragmentation techniques that can distinguish aspartic acid from its isomer, isoaspartic acid, were compared. MALDI post-source decay (PSD), MALDI 157 nm photodissociation, tris(2,4,6-trimethoxyphenyl)phosphonium bromide (TMPP) charge tagging in PSD and photodissociation, ESI collision-induced dissociation (CID), electron transfer dissociation (ETD), and free-radical initiated peptide sequencing (FRIPS) with CID were applied to peptides containing either aspartic or isoaspartic acid. Diagnostic ions, such as the y-46 and b+H2O, are present in PSD, photodissociation, and charge tagging. c•+57 and z-57 ions are observed in ETD and FRIPS experiments. For some molecules, aspartic and isoaspartic acid yield ion fragments with significantly different intensities. ETD and charge tagging appear to be most effective at distinguishing these residues. Graphical Abstract ᅟ.
Department of Chemistry, Indiana University, 800 East Kirkwood Avenue, Bloomington, IN, 47405, USA.
Nick
N
DeGraan-Weber
Pre-Pivotal Drug Product Technologies, Amgen Inc., Thousand Oaks, CA, 91320, USA.
Jun
J
Zhang
Department of Chemistry, Indiana University, 800 East Kirkwood Avenue, Bloomington, IN, 47405, USA. reilly@indiana.edu.
James P
JP
Reilly
D000595:Amino Acid Sequence; D007477:Ions; D026581:Isoaspartic Acid / Q000032:analysis*; D013058:Mass Spectrometry; D010455:Peptides / Q000032:analysis*
D007477:Ions; D026581:Isoaspartic Acid; D010455:Peptides
CID; Charge tagging; ETD; FRIPS; Isoaspartic acid; PSD; Peptide fragmentation; Photodissociation