Mass Spectrometric Evidence for the Existence of Distinct Modifications of Different Proteins by 2(E),4(E)-Decadienal

2(E),4(E)-Decadienal (DDE), a lipid peroxidation product, was found to covalently modify Lys residues of different proteins by different reactions using mass spectrometry (MALDI-TOF-MS and LC-ESI-MS). DDE mainly formed Lys Schiff base adducts with cytochrome c and ribonuclease A at 10 min, but these reversibly formed adducts almost disappeared after 24 h. In contrast, beta-lactoglobulin (beta-LG) was highly modified by DDE after 24 h. In addition to the Lys Schiff base adducts, DDE formed novel Lys pyridinium adducts as well as Cys Michael adducts with beta-LG.