A novel multifunctional labeling reagent for enhanced protein characterization with mass spectrometry

Individual peptides with lysine at the C‐terminus as well as protein tryptic digests were reacted with 2‐methoxy‐4,5‐dihydro‐1H‐imidazole, converting lysine residues to their 4,5‐dihydro‐1H‐imidazol‐2‐yl derivatives. The mass spectra of derivatized digests exhibit a greater number of more intense features than their underivatized counterparts, thus increasing the information obtained in peptide mapping experiments. Additionally, MS/MS spectra of the derivatized peptides are greatly simplified in comparison to their native species, yielding primarily an easily interpretable series of y‐ions. Finally, this novel label also enables differential quantitation studies, as a stable isotopic form containing four deuterium atoms can readily be produced. Copyright © 2001 John Wiley & Sons, Ltd.