ε‐N,N,N‐Trimethyllysine‐specific ions in matrix‐assisted laser desorption/ionization‐tandem mass spectrometry

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Abstract
ε-N,N,N-Trimethyllysine (Kme3) is a component of a number of proteins and plays an important role in the expression of their biological functions. Trimethylation, which causes an incremental increase in mass of 42.0470 Da from that of the corresponding MH+ ion, cannot be distinguished from the acetylation (+42.0106 Da), which also occurs on ε-amino groups of Lys or α-amino groups in many proteins, without high-accuracy mass measurement which is accurate to within the second decimal place. MALDI-MS and MS/MS have been applied for the analyses of post-translational modifications of histone H3, which is known to contain both multiple acetylation and methylation sites in its sequence. During the measurements of the modified peptides, a novel fragmentation which involves the loss of trimethylamine from Kme3 was found. This characteristic fragmentation, which was observed to produce ions separated by 59 Da from the conventional precursor ion or sequence ions, would be useful for probing Kme3 units in the sequence. Copyright © 2003 John Wiley & Sons, Ltd.