Enzymatic Synthesis of Isotopically Labeled Hydrogen Peroxide for Mass Spectrometry-Based Applications.

Methionine oxidation is involved in multiple biological processes including protein misfolding and enzyme regulation. However, it is often challenging to measure levels of methionine oxidation by mass spectrometry, in part due to the prevalence of artifactual oxidation that occurs during the sample preparation and ionization steps of typical proteomic workflows. Isotopically labeled hydrogen peroxide (H(2)(18)O(2)) can be used to block unoxidized methionines and enables accurate measurement of in vivo levels of methionine oxidation. However, H(2)(18)O(2) is an expensive reagent that can be difficult to obtain from commercial sources. Here, we report a method for synthesizing H(2)(18)O(2) in-house. Glucose oxidase catalyzes the oxidation of β-d-glucose and produces hydrogen peroxide in the process. We took advantage of this reaction to enzymatically synthesize H(2)(18)O(2) from (18)O(2) and assessed its concentration, purity, and utility in measuring methionine oxidation levels by mass spectrometry.