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J Am Soc Mass Spectrom. 2012 Apr;23(4):608-20. doi: 10.1007/s13361-011-0184-y. Epub 2011 Jun 23.

Tunable charge tags for electron-based methods of peptide sequencing: design and applications.

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Department of Chemistry, University of Washington, Bagley Hall, Box 351700, Seattle, WA 98195-1700, USA.


Charge tags using basic auxiliary functional groups 6-aminoquinolinylcarboxamido, 4-aminopyrimidyl-1-methylcarboxamido, 2-aminobenzoimidazolyl-1-methylcarboxamido, and the fixed-charge 4-(dimethylamino)pyridyl-1-carboxamido moiety are evaluated as to their properties in electron transfer dissociation mass spectra of arginine C-terminated peptides. The neutral tags have proton affinities that are competitive with those of amino acid residues in peptides. Charge reduction by electron transfer from fluoranthene anion-radicals results in peptide backbone dissociations that improve sequence coverage by providing extensive series of N-terminal c-type fragments without impeding the formation of C-terminal z fragments. Comparison of ETD mass spectra of free and tagged peptides allows one to resolve ambiguities in fragment ion assignment through mass shifts of c ions. Simple chemical procedures are reported for N-terminal tagging of Arg-containing tryptic peptides.

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