Sequencing of Peptides by SIMS from the C or N Terminus

A novel method has been developed to sequence proteins and peptides from either the C or N terminus using secondary ion mass spectrometry (SIMS) [1]. Unlike other mass spectrometric methods, fragmentation during ionization or desorption in the mass spectrometer is not relied upon. Instead, this method is based on observations by Cooks and coworkers [2] that the emission of ‘preformed ions’ is greatly enhanced over that of non-charged species. If a peptide is labeled at either the N or C terminus with a charged moiety and randomly cleaved with acid or enzymes, only the products with the charged grouping are observed in the SIMS spectrum of the mixture. The sensitivity for some peptides is in the picomole range.