157 nm Photodissociation of Dipeptide Ions Containing N-Terminal Arginine

Abstract

Twenty singly-charged dipeptide ions with N-terminal arginine were photodissociated using 157 nm light in both a linear ion-trap mass spectrometer and a MALDI-TOF-TOF mass spectrometer. Analogous to previous work on dipeptides containing C-terminal arginine, this set of samples enabled insights into the photofragmentation propensities associated with individual residues. In addition to familiar products such as a-, d-, and immonium ions, m2 and m2+13 ions were also observed. Certain side chains tended to cleave between their β and γ carbons without necessarily forming d- or w-type ions, and a few other ions were produced by the high-energy fragmentation of multiple bonds.

Charge Transfer Dissociation (CTD) Mass Spectrometry of Peptide Cations Using Kiloelectronvolt Helium Cations

“…Figure 3 shows the isolated monoisotopic precursor along with the a 7 and a 8 ions with the a + 1 ions marked. The same a + 1 ions have been seen with UVPD [18,52], and metastable atom activated dissociation [25], when the peptide contains a basic residue at the N terminus. Conventional (low energy) CID of peptides containing a lysine residue at the N terminus shows poor yields of a ions [52], but UVPD was able to significantly improve the production.…”

“…The a + 1 ions are thought to arise from the homolytic cleavage of the C-C α bond along the backbone [50]. Subsequent elimination of a hydrogen radical results in the formation of even electron a-type ions [15,18]. Figure 3 shows the isolated monoisotopic precursor along with the a 7 and a 8 ions with the a + 1 ions marked.…”

“…Oftentimes, CID does not provide complete fragmentation of the peptide backbone and results in significant side-chain losses, including the loss of post-translational modifications, and thereby complicates the interpretation of tandem mass spectra [4,5]. These limitations have fueled a significant investment in alternative fragmentation techniques, including electron transfer dissociation (ETD) with cationic [6][7][8][9] or anionic [6,10] precursor ions, electron capture dissociation (ECD) with cationic [9,11], or anionic precursor ions [12], photodissociation [13][14][15][16][17][18][19][20], metastable atom-activated dissociation (MAD) [21][22][23][24][25][26][27][28], electron ionization dissociation (EID) [29], and electron detachment dissociation (EDD) [30]. Each technique has its merits and limitations.…”

“…Each technique has its merits and limitations. Photodissociation techniques require a chromophore that can absorb at the incident wavelength to initiate fragmentation, and such chromophores can be relatively nonselective amide bonds [13][14][15][16][17][18][19][20] or highly site-selective [31][32][33]. Chromophores can also include specific and native chromophores like disulfide bonds [34] but non-native chromophores are dependent on the ability to chemically modify the peptides or proteins of interest.…”

Ion Activation Methods for Peptides and Proteins

“…Reilly’s group, in particular, has undertaken the most extensive studies to elucidate UVPD mechanisms and pathway, thus justifying that UVPD entails photolytic radical cleavage of the C - C α bond prior to radical elimination to form a/x-type ions and other subsequent products. 86,96–100 …”