On the mechanism of electron-capture-induced dissociation of peptide dications from 15n-labeling and crown-ether complexation.
15N-labeling of di- and tripeptides reveals that electron capture to doubly protonated peptides results almost exclusively in ammonia loss from the N-terminal end, which clearly shows that a significant fraction of electron capture occurs at this end. In accordance with this finding, the competing channel of N-Calpha bond breakage leads to z+* ions and neutral c fragments after electron capture to small dications. In larger peptides that live long enough for internal proton exchanges to occur, c+ ions are also formed and in some cases in dominant yield. Attachment of one or two crown ethers to ammonium groups is likely to reduce the probability of proton transfer, which enhances the formation of z+* relative to c+. The total yield of z+* and c+ is, however, more or less unchanged, which indicates that proton transfer or hydrogen transfer from a NH3 group to the amide group is not required for the N-Calpha bond breakage.
Holm
Anne I S
AI
Department of Physics and Astronomy, University of Aarhus, Ny Munkegade, DK-8000 Aarhus C, Denmark, School of Physics and Electronics, Henan University, Kaifeng, 475001, China.
Hvelplund
Preben
P
Kadhane
Umesh
U
Larsen
Mikkel Koefoed
MK
Liu
Bo
B
Nielsen
Steen Brøndsted
SB
Panja
Subhasis
S
Pedersen
Jan Mondrup
JM
Skrydstrup
Troels
T
Støchkel
Kristian
K
Williams
Evan R
ER
Worm
Esben S
ES