Valence parity renders z(*)-type ions chemically distinct

Area of Science:

• Proteomics
• Mass Spectrometry
• Chemical Analysis

Background:

• Electron-based peptide dissociation methods like electron capture dissociation (ECD) and electron transfer dissociation (ETD) produce various product ions.
• Understanding the chemical composition of these product ions is crucial for accurate peptide analysis.

Purpose of the Study:

• To report a novel valence parity rule governing the formation of z (*)-type ions.
• To demonstrate how this rule differentiates z (*)-type ions from other common product ions, particularly c-type ions.
• To show the practical application of this rule in peptide analysis.

Main Methods:

• Analysis of 226 electron transfer dissociation (ETD) product ion spectra.
• Applying the valence parity rule to assign chemical compositions and ion types to observed product ions.
• Experimental validation of the rule's predictive power.

Main Results:

• z (*)-type ions possess an even number of atoms with odd valence, distinct from b-, c-, and y-type ions.
• The valence parity rule dictates that c-type and z (*)-type ions cannot share the same chemical composition or mass.
• Nearly half of observed c- and z (*)-type ions were correctly assigned by simple inspection of m/z peaks.

Conclusions:

• The valence parity rule provides a straightforward method for distinguishing c- and z (*)-type ions.
• This rule facilitates direct determination of amino acid composition.
• The findings offer a basis for improved database search algorithms and de novo peptide sequencing.