Oxygen exchange may occur at carboxyl groups catalyzed by acid. The reaction, however, takes at least several days at room temperature. The long-time exchanging reaction often prevents its application from protein analysis. In this study, an 18O-labeling method utilizing microwave-assisted acid hydrolysis was developed. After being dissolved in 16O/18O (1:1) water containing 2.5% formic acid, protein samples were exposed to microwave irradiation. LC-MS/MS analysis of the resulted peptide mixtures indicated that oxygen in the carboxyl groups from glutamic acid, aspartic acid, and the C-terminal residues could be efficiently exchanged with 18O within less than 15 min. The rate of back exchange was so slow that no detectable back exchange could be found during the HPLC run.
Scopus Subject Areas
- Analytical Chemistry