Free Radical–Initiated Peptide Sequencing Mass Spectrometry for Phosphopeptide Post-translational Modification Analysis

  • Inae Jang
  • Aeran Jeon
  • Suk Gyu Lim
  • Duk Ki Hong
  • Min Soo Kim
  • Jae Hyeong Jo
  • Sang Tak Lee
  • Bongjin Moon
  • Han Bin OhEmail author
Research Article


Free radical–initiated peptide sequencing mass spectrometry (FRIPS MS) was employed to analyze a number of representative singly or doubly protonated phosphopeptides (phosphoserine and phosphotyrosine peptides) in positive ion mode. In contrast to collision-activated dissociation (CAD) results, a loss of a phosphate group occurred to a limited degree for both phosphoserine and phosphotyrosine peptides, and thus, localization of a phosphorylated site was readily achieved. Considering that FRIPS MS supplies a substantial amount of collisional energy to peptides, this result was quite unexpected because a labile phosphate group was conserved. Analysis of the resulting peptide fragments revealed the extensive production of a-, c-, x-, and z-type fragments (with some minor b- and y-type fragments), suggesting that radical-driven peptide fragmentation was the primary mechanism involved in the FRIPS MS of phosphopeptides. Results of this study clearly indicate that FRIPS MS is a promising tool for the characterization of post-translational modifications such as phosphorylation.

Graphical Abstract


Free radical–initiated peptide sequencing (FRIPS) Radical-driven tandem mass spectrometry Phosphopeptides Phosphorylation Post-translational modifications (PTMs) 



This work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2015R1D1A1A01056782 and 2018R1A6A1A03024940).

Supplementary material

13361_2018_2100_MOESM1_ESM.docx (566 kb)
ESM 1 (DOCX 566 kb)


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Copyright information

© American Society for Mass Spectrometry 2018

Authors and Affiliations

  1. 1.Department of ChemistrySogang UniversitySeoulRepublic of Korea
  2. 2.Seoul Science High SchoolSeoulRepublic of Korea
  3. 3.Seoul National UniversitySeoulRepublic of Korea
  4. 4.Korea UniversitySeoulRepublic of Korea
  5. 5.Korea Advanced Institute of Science and TechnologyDaejeonRepublic of Korea

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