Oxidation of peptides during electrospray ionization

Area of Science:

• Analytical Chemistry
• Mass Spectrometry
• Proteomics

Background:

• Electrospray ionization (ESI) is a common technique for peptide analysis.
• Oxidation of specific amino acid residues can occur during mass spectrometry.
• Understanding these modifications is crucial for accurate peptide identification.

Purpose of the Study:

• To investigate the cause and implications of a +16 Da mass shift observed in ESI mass spectrometry.
• To determine the specific amino acid residues susceptible to this oxidation.
• To explore the utility of this oxidative modification in peptide analysis.

Main Methods:

• Analysis of synthetic and natural peptides using electrospray ionization mass spectrometry (ESI-MS).
• Investigation of the influence of electrospray parameters (field strength, flow rate) on the modification.
• Confirmation using tandem mass spectrometry (MS/MS) experiments.
• Application to the analysis of tryptic digests, exemplified by myoglobin.

Main Results:

• A +16 Da modification, identified as selective oxidation, was observed in peptides containing methionyl, tryptophanyl, or tyrosyl residues.
• The oxidation is dependent on electrospray conditions.
• Tandem mass spectrometry confirmed the oxidation site.
• The [M + H + 16]+ ion aided in identifying tryptic fragments of myoglobin.

Conclusions:

• The +16 Da oxidation is a common phenomenon in ESI-MS of peptides with oxidizable residues.
• Care must be taken during analysis to account for this potential modification.
• The selective oxidation can be strategically employed to enhance peptide identification and characterization.