Evidence for Sequence Scrambling and Divergent H/D Exchange Reactions of Doubly-Charged Isobaric b-Type Fragment Ions

  • Behrooz Zekavat
  • Mahsan Miladi
  • Abdullah H. Al-Fdeilat
  • Arpad Somogyi
  • Touradj SoloukiEmail author
Research Article


To date, only a limited number of reports are available on structural variants of multiply-charged b-fragment ions. We report on observed bimodal gas-phase hydrogen/deuterium exchange (HDX) reaction kinetics and patterns for substance P b10 2+ that point to presence of isomeric structures. We also compare HDX reactions, post-ion mobility/collision-induced dissociation (post-IM/CID), and sustained off-resonance irradiation-collision induced dissociation (SORI-CID) of substance P b10 2+ and a cyclic peptide with an identical amino acid (AA) sequence order to substance P b10. The observed HDX patterns and reaction kinetics and SORI-CID pattern for the doubly charged head-to-tail cyclized peptide were different from either of the presumed isomers of substance P b10 2+, suggesting that b10 2+ may not exist exclusively as a head-to-tail cyclized structure. Ultra-high mass measurement accuracy was used to assign identities of the observed SORI-CID fragment ions of substance P b10 2+; over 30 % of the observed SORI-CID fragment ions from substance P b10 2+ had rearranged (scrambled) AA sequences. Moreover, post-IM/CID experiments revealed the presence of two conformer types for substance P b10 2+, whereas only one conformer type was observed for the head-to-tail cyclized peptide. We also show that AA sequence scrambling from CID of doubly-charged b-fragment ions is not unique to substance P b10 2+.

Key words

b-Fragment FT-ICR Gas-phase H/D exchange (HDX) Kinetics Sequence scrambling Post-IM/CID SORI-CID 



The authors gratefully acknowledge the financial support from the Institute for Therapeutic Discovery (Delanson, NY, USA) and Baylor University.

Supplementary material

13361_2013_768_MOESM1_ESM.docx (4.6 mb)
ESM 1 (DOCX 4664 kb)


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Copyright information

© American Society for Mass Spectrometry 2013

Authors and Affiliations

  • Behrooz Zekavat
    • 1
  • Mahsan Miladi
    • 1
  • Abdullah H. Al-Fdeilat
    • 2
  • Arpad Somogyi
    • 3
  • Touradj Solouki
    • 1
    Email author
  1. 1.Department of Chemistry and BiochemistryBaylor UniversityWacoUSA
  2. 2.Department of ChemistryUniversity of MaineOronoUSA
  3. 3.Department of Chemistry and BiochemistryUniversity of ArizonaTucsonUSA

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