Intramolecular Hydrogen Transfer from the Alpha-Carbon (Cα) and Backbone Amide Nitrogen (Nb) to Form c- and y-Ions in Negative-Ion CID of Peptides

• Published in: Journal of the American Society for Mass Spectrometry 2019-09, Vol.30 (9), p.1592-1600
• Main Authors: Kagoshima, Asaki, Sekimoto, Kanako, Takayama, Mitsuo
• Format: Article
• Language: English
• Subjects: ABSORPTION SPECTROSCOPY; Amides - chemistry; Analytical Chemistry; ATOMIC AND MOLECULAR PHYSICS; Backbone; Bioinformatics; Biotechnology; CARBON; Chemistry; Chemistry and Materials Science; Deuteration; DEUTERIUM; Deuterium - chemistry; HYDROGEN; Hydrogen - chemistry; HYDROGEN TRANSFER; Ions - chemistry; MASS SPECTROMETERS; Mass spectrometry; MOLECULES; NITROGEN; Organic Chemistry; PEPTIDES; Peptides - analysis; Peptides - chemistry; Proteomics; Research Article; RESOLUTION; Spectrometry, Mass, Electrospray Ionization - methods
• ISSN: 1044-0305; 1879-1123
• DOI: 10.1007/s13361-019-02245-z

The source of hydrogen in the formation of c- and y-ions produced by intramolecular hydrogen transfer in negative-ion CID experiments with peptides has been examined using Cα-, Cβ-, and backbone amide (N b )-deuterated peptides AAA(d3)AA, AAG(d2)AA, AAAG(d2)A, and AAAAA-d7, as well as five other peptides. The c- and y-ions produced by deuterium transfer from the deuterated residues were detected and identified by the exact m/z values obtained with a high-resolution orbitrap mass spectrometer. The rate of deuterium transfer obtained indicates that over 50% of the hydrogen was originated from the backbone amide nitrogen, with the residual hydrogen coming from the backbone Cα. It is clear that the hydrogen does not originate from the side chain Cβ. It is hypothesized that the intramolecular hydrogen transfer to form negative c- and y-ions takes place via 3-, 4-, 6-, 7-, 8-, and 9-membered ring transition states.