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.