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International Journal of Analytical Chemistry
Volume 2009, Article ID 153472, 13 pages
Research Article

LC/MS/MS Analysis of N-Terminal Protein Adducts with Improved Sensitivity: A Comparison of Selected Edman Isothiocyanate Reagents

1Arrhenius Laboratory, Department of Environmental Chemistry, Stockholm University, 106 91 Stockholm, Sweden
2Department of Applied Environmental Science, Stockholm University, 106 91 Stockholm, Sweden
3PerkinElmer Sverige AB, Oxfordhuset, Johanneslundsvägen 2, 194 81 Upplands Väsby, Sweden

Received 22 April 2009; Accepted 1 August 2009

Academic Editor: Shoji Motomizu

Copyright © 2009 Per Rydberg et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


This study provides a basis for a new and straightforward method for LC/MS/MS-based screening of N-terminal protein adducts. This procedure is denoted the “FI E procedure” as fluorescein sothiocyanate (FITC) gave superior sensitivity by LC/MS/MS when measuring adducts ( ) of electrophilic compounds with a modified Edman procedure. The principles of the FI E- are that adducts to N-terminal amino acids selectively are detached and measured from of proteins after derivatisation by isothiocyanate Edman reagents. In this study, FITC, 4-N,N-dimethylaminoazobenzene -isothiocyanate (DABITC) and 4-dimethylamino-1-naphthyl isothiocyanate (DNITC) were used to synthesize thiohydantoin analytes from valine and N-methylvaline. The sensitivity by LC/MS/MS was enhanced by up to three orders of magnitude as compared to phenyl isothiocyanate and higher as compared to pentafluorophenyl isothiocyanate. The FITC reagent will enable measurements of low background adduct levels. Synthesized analytes were characterised with, for example, NMR, NMR, LC/MS/MS, and UV.