Fragmentation of alpha-radical cations of arginine-containing peptides.
Fragmentation pathways of peptide radical cations, M(+*), with well-defined initial location of the radical site were explored using collision-induced dissociation (CID) experiments. Peptide radical cations were produced by gas-phase fragmentation of Co(III)(salen)-peptide complexes [salen = N,N'-ethylenebis (salicylideneiminato)]. Subsequent hydrogen abstraction from the beta-carbon of the side-chain followed by C(alpha)-C(beta) bond cleavage results in the loss of a neutral side chain and formation of an alpha-radical cation with the radical site localized on the alpha-carbon of the backbone. Similar CID spectra dominated by radical-driven dissociation products were obtained for a number of arginine-containing alpha-radicals, suggesting that for these systems radical migration precedes fragmentation. In contrast, proton-driven fragmentation dominates CID spectra of alpha-radicals produced via the loss of the arginine side chain. Radical-driven fragmentation of large M(+*) peptide radical cations is dominated by side-chain losses, formation of even-electron a-ions and odd-electron x-ions resulting from C(alpha)-C bond cleavages, formation of odd-electron z-ions, and loss of the N-terminal residue. In contrast, charge-driven fragmentation produces even-electron y-ions and odd-electron b-ions.
Laskin
Julia
J
Chemical and Materials Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, USA. Julia.Laskin@pnl.gov
Yang
Zhibo
Z
Ng
C M Dominic
CM
Chu
Ivan K
IK
D001120:Arginine / Q000737:chemistry*; D002412:Cations; D005609:Free Radicals / Q000737:chemistry; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D008956:Models, Chemical; D010455:Peptides / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
D002412:Cations; D005609:Free Radicals; D010455:Peptides; D001120:Arginine