Enhancing the intensities of lysine-terminated tryptic peptide ions in matrix-assisted laser desorption/ionization mass spectrometry.

Tryptic digests of three proteins are reacted with O-methylisourea in order to convert lysine residues to homoarginines. The resulting homoarginine-terminated peptides exhibit more intense MALDI mass spectral peaks than their lysine-terminated predecessors. This simple chemical reaction should therefore facilitate protein sequencing and mass mapping.