Sequence determination ofN-acetylated-N,O-permethylated peptides by plasma desorption mass spectrometry

The plasma desorption mass spectra of N-acetylated-N,O-permethylated peptides contain sufficient fragment ions to allow partial or complete sequence determination. By optimization of the derivatization procedure and an inclusion of a purification step by high-performance liquid chromatrography (HPLC) overall sensitivities on the high picomole level are obtained. By using limiting derivatization conditions the fully derivatized peptide is easily selected from the HPLC separation. Mainly N-terminal sequence ions are observed, facilitating sequence determination of naturally N-blocked peptides. Complete sequence determination of naturally formylated gramicidin A containing 15 amino acid residues and the naturally N-acetylated N-terminal heptapeptide from an acyl-CoA binding protein is demonstrated. The sequence of the first six N-terminal residues was obtained by derivatization of the A-chain of insulin.