Discrimination of Isobaric Leu/Ile Residues by MALDI In-Source Decay Mass Spectrometry
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MALDI in-source decay (ISD) has been used for top-down sequencing of proteins. The use of the matrix 1,5-diaminonapthalene (1,5-DAN) gave abundant w ions, which are formed from the unimolecular dissociation of z• radical fragments via α cleavage reaction and thus help identify which of the isobaric amino acids, Leu or Ile, is present. The high abundance of w ions in MALDI-ISD with 1,5-DAN results from the low collision rate in the MALDI plume. MALDI-ISD with 1,5-DAN appears to be an useful method for the top-down sequencing of proteins, including discrimination of Leu and Ile near the C-terminal end.
Key wordsInitial velocity Side-chain loss 1,5-Diaminonapthalene Negative-ion mode Top-down sequencing
D.A. acknowledges a research fellowship from the Japan Society for the Promotion of Science for Young Scientists (grant 23-10272). N.S. is a FRS-FNRS logistics collaborator. Walloon Region and FNRS contributed to Mass Spectrometry platform funding.
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