title: Valence parity renders z(*)-type ions chemically distinct.
abstract: Here we report that the odd electron z (*) -type ions formed by the electron-based peptide dissociation methods (electron capture or transfer, ECD or ETD) have distinctive chemical compositions from other common product ion types. Specifically, b-, c-, and y-type ions have an odd number of atoms with an odd valence (e.g., N and H), while z (*)-type ions contain an even number of atoms with an odd valence. This tenet, referred to as the valence parity rule, mandates that no c-type ion shall have the same chemical composition, and by extension mass, as a z (*) -type ion. By experiment we demonstrate that nearly half of all observed c- and z (*) -type product ions resulting from 226 ETD product ion spectra can be assigned to a single, correct, chemical composition and ion type by simple inspection of the m/ z peaks. The assignments provide (1) a platform to directly determine amino acid composition, (2) an input for database search algorithms, or (3) a basis for de novo sequence analysis.
authors.affiliation: Department of Mathematics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors.forename: Shane L
authors.initials: SL
authors.lastname: Hubler
authors.forename: April
authors.initials: A
authors.lastname: Jue
authors.forename: Jason
authors.initials: J
authors.lastname: Keith
authors.forename: Graeme C
authors.initials: GC
authors.lastname: McAlister
authors.forename: Gheorghe
authors.initials: G
authors.lastname: Craciun
authors.forename: Joshua J
authors.initials: JJ
authors.lastname: Coon
mesh_terms: D000596:Amino Acids / Q000737:chemistry; D005583:Fourier Analysis; D007477:Ions / Q000737:chemistry; D010449:Peptide Mapping; D010455:Peptides / Q000032:analysis / Q000737:chemistry*; D053719:Tandem Mass Spectrometry / Q000379:methods*; D015003:Yeasts / Q000737:chemistry
chemical_list: D000596:Amino Acids; D007477:Ions; D010455:Peptides