Rapid determination of oxidized methionine residues in recombinant human basic fibroblast growth factor by ultra‐performance liquid chromatography and electrospray ionization quadrupole time‐of‐flight mass spectrometry with in‐source collision‐induced dissociation

The primary structure of the deteriorated recombinant human basic fibroblast growth factor (rhbFGF) was determined by ultra‐performance liquid chromatography and electrospray ionization quadrupole time‐of‐flight mass spectrometry (UPLC/ESI‐QTOF‐MS) with in‐source collision‐induced dissociation (CID). The rhbFGFs before and after treatment with hydrogen peroxide (H₂O₂) were separated using an ACQUITY UPLC BEH300 C18 column (1.7 µm, 150 mm × 2.1 mm i.d.) with a gradient elution of a mixture of water/acetonitrile containing 0.1% formic acid. The separated proteins were then detected by a SYNAPT? High Definition Mass Spectrometry? system (SYNAPT‐MS). Two methionine (Met) residues in the rhbFGF structure were oxidized to Met‐sulfoxide (Met‐O) in 0.03% H₂O₂ at pH 2.0. As the result, three peaks, except for the peak of rhbFGF, appeared on the chromatogram. The three proteins corresponding to each peak were estimated as the denatured rhbFGFs including the Met‐O residue(s) with TOF‐MS. Furthermore, the position of the Met‐O residue(s) was efficiently identified by UPLC/ESI‐QTOF‐MS using the in‐source CID technique. The proposed method seems to be very useful for the structural elucidation of proteins, because the oxidized Met residues in rhbFGF were easily and rapidly identified. Copyright © 2009 John Wiley & Sons, Ltd.