Andreazza, H.Bowie, J.2011-04-052011-04-052010Physical Chemistry Chemical Physics, 2010; 12(41):13400-134071463-90761463-9084http://hdl.handle.net/2440/62933Negative ion electrospray mass spectra of the peptides produced by tryptic and chymotrypsin digests of bovine insulin, and from the tryptic digest of lysozyme identify at least 80% of the sequences of these proteins. In particular, negative ion mass spectrometry identifies and positions disulfide moieties, and is the method of choice for identifying this post-translational modification in these two proteins. Intramolecular disulfide functionality is identified by the fragmentation [(M − H)− − H2S2]− in a digest peptide, and CID of that fragment anion provides amino acid sequencing information. Digest peptides containing an intermolecular disulfide structure undergo facile and diagnostic cleavages. Each cleavage produces a peptide fragment from which CID MS/MS data provide sequencing information.en© 2010 Royal Society of ChemistryAnimalsCattleDisulfidesInsulinMuramidaseTrypsinSpectrometry, Mass, Electrospray IonizationSequence Analysis, ProteinAmino Acid SequenceMolecular Sequence DataJournal article002010111110.1039/C0CP00717J0002829724000072-s2.0-7795811082333136