Characterization of chemical modification of tryptophan by matrix-assisted laser desorption/ionization mass spectrometry.

Tert- butylation of tryptophan (2', 5', 7'- tri tertiary butyl tryptophan), formed during acidolytic cleavage of synthetic peptides Ac-KLVYWAE-CONH(2) (A-YW) and Ac-KLVWWAE-CONH(2) (A-WW), that are analogs of the fragment of Alzheimer's beta-amyloid peptide Ac-KLVFFAE-CONH(2), during solid-phase peptide synthesis, was characterized by matrix-assisted laser desorption/ionization time of flight/time of flight (MALDI TOF/TOF) mass spectrometry. Crude peptide was fractionated by high performance liquid chromatography. Peptide fractions were sequenced and modified tryptophan was determined with the help of MALDI TOF/TOF mass spectra. Thus, it is possible to pinpoint the particular tryptophan residue that undergoes modification during synthesis of peptides containing multiple tryptophan residues.