Quantitative analysis of in vivo methionine oxidation of the human proteome

A novel stable isotope labelling stategy was developed to quantify methionine oxidation in an unstressed human proteome. Cell extracts were oxidized with 18O labelled hydrogen peroxide following cell lysis in order to convert all unoxidized methionine residues to an oxidized version with a heavy label. The heavy labelled peptides were used to generate a custom search and quantification of the relative ratios between heavy and light labelled methionine sulfoxide containing peptides. Where the light labelled peptides were in vivo oxidized