Neutral loss of water from the b ions with histidine at the C-terminus and formation of the c ions involving lysine side chains.
Neutral loss of water from the amide bond induced by the His side chain has been reported. The proposed fragmentation pathway is a retro-Ritter reaction catalyzed by the imidazole nitrogen. In our MS/MS study of the neuropeptide GAHKNYLRFamide, we observed that the neutral loss of water from the b(3) ion is abundant. The b(3) ion has a His residue at the C-terminus. As reported previously, in the b ions with His at the C-terminus, the imidazole residue is connected to the carbonyl carbon to form a five-membered ring. Therefore, it is unlikely that the neutral loss of water from the b(3) ion is catalyzed by the imidazole nitrogen. Through MS2 and MS3 studies of a synthetic peptide standard AGHKLL and its chemically labeled and isotope-encoded forms, we discovered that the water loss from the b(3) ion involves the carbonyl group of His, the hydrogen connected to the alpha-carbon of Gly, and the amide hydrogen of His. We also discovered the formation of an unusual c(x) ion in peptides with a Lys or Arg residue at the (x + 1) position of the peptide.
Fu
Qiang
Q
Department of Chemistry, University of Wisconsin, 1101 University Avenue, Madison, Wisconsin 53706, USA.
Li
Lingjun
L
D000107:Acetylation; D000577:Amides / Q000737:chemistry; D019835:FMRFamide / Q000737:chemistry*; D006639:Histidine / Q000737:chemistry*; D007477:Ions / Q000737:chemistry; D008239:Lysine / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D014867:Water / Q000737:chemistry*
D000577:Amides; C511157:GAHKNYLRFamide; D007477:Ions; D014867:Water; D006639:Histidine; D019835:FMRFamide; D008239:Lysine