DIRECT OBSERVATION OF PROTEIN GLYCOSYLATION BY MATRIX-ASSISTED LASER-DESORPTION IONIZATION TIME-OF-FLIGHT MASS-SPECTROMETRY

Nonenzymatic glycosylation products of several peptides and lysozyme w ere observed directly by matrix-assisted laser desorption/ionization t ime-of-flight mass spectrometry (MALDI-TOF-MS) operating in a linear m ode, and the number of glucose units added was determined from the obs erved mass. Oxidation products of the peptides and the glycosylated pe ptides were also observed. Lysine residues were readily glycosylated; however, a nonapeptide without lysine residue also showed addition of up to four glucose units, suggesting that other amino acid residues ca n also be glycosylated. The MALDI-TOF-MS technique was useful for comp aring reaction products from the glycosylation of different peptides a s well as for demonstrating inhibition of glycosylation by N-alpha-ace tyl-L-lysine.