Lysozyme oxidation by singlet molecular oxygen: Peptide characterization using [ O]-labeling oxygen and nLC-MS/MS.

Singlet molecular oxygen ( O ) is generated in biological systems and reacts with different biomolecules. Proteins are a major target for O , and His, Tyr, Met, Cys, and Trp are oxidized at physiological pH. In the present study, the modification of lysozyme protein by O was investigated using mass spectrometry approaches. The experimental findings showed methionine, histidine, and tryptophan oxidation. The experiments were achieved using [ O]-labeled O released from thermolabile endoperoxides in association with nano-scale liquid chromatography coupled to electrospray ionization mass spectrometry. The structural characterization by nLC-MS/MS of the amino acids in the tryptic peptides of the proteins showed addition of [ O]-labeling atoms in different amino acids.