Sequence determination of N-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.