A novel mass spectrometric approach to the analysis of hormonal peptides in extracts of mouse pancreatic islets.

Liquid chromatography mass spectrometry (LC-MS) is a valuable tool in the analysis of proteins and peptides. The combination of LC-MS with different fragmentation methods provides sequence information on components in complex mixtures. In this work, on-line packed capillary LC electrospray ionization Fourier transform ion cyclotron resonance MS was combined with two complementary fragmentation techniques, i.e. nozzle-skimmer fragmentation and electron capture dissociation, for the determination of hormonal peptides in an acid ethanol extract of mouse pancreatic islets. The most abundant peptides, those derived from proinsulin and proglucagon, were identified by their masses and additional sequence-tag information established their identities. Interestingly, the experiments demonstrated the presence of truncated C-peptides, des-(25-29)-C-peptide and des-(27-31)-C-peptide. These novel findings clearly illustrate the potential usefulness of the described technique for on-line sequencing and characterization of peptides in tissue extracts.