Tandem mass spectrometry of peptides: Mechanistic aspects and structural information based on neutral losses. II—Tri- and larger peptides

✍ Scribed by Marcela M. Cordero; Chrys Wesdemiotis

• Publisher: John Wiley and Sons
• Year: 1994
• Tongue: English
• Weight: 717 KB
• Volume: 29
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/oms.1210290709

✦ Synopsis

Abstract

The neutral products arising during the collisionally activated dissociation of protonated oligopeptides (MH^+^) are post‐ionized by collision and detected in neutral fragment‐reionization (^+^N~f~R^+^) mass spectra. For the isomeric tripeptides Ala‐Gly‐Gly, Gly‐Ala‐Gly and Gly‐Gly‐Ala, the amino acid and dipeptide losses from the C‐terminus and the diketopiperazine losses from the N‐terminus allow for differentiation. These neutral fragments are identified in the corresponding ^+^N~f~R^+^ spectra by comparison to reference collision‐induced dissociative ionization (CIDI) mass spectra of individual amino acids, dipeptides and diketopiperazines. Peptides with distinct C‐termini but otherwise identical sequences are found to yield ^+^N~f~R^+^ products that are characteristic of the respective C‐terminal amino acid. This is demonstrated for several peptide pairs, including leucine‐ and methionine‐enkephalin. In general, ^+^N~f~R^+^ spectra are dominated by the heavier neutral losses; further, ^+^N~f~R^+^ and CIDI cause extensive dissociation, indicating that the collisional ionization process imparts high average internal energies.