Bilusich, D.Maselli, V.Brinkworth, C.Samguina, T.Lebedev, A.Bowie, J.2007-02-252007-02-252005Rapid Communications in Mass Spectrometry, 2005; 19(21):3063-30740951-41981097-0231http://hdl.handle.net/2440/17807The definitive version may be found at www.wiley.com[M--H]- parent anions of underivatised peptides containing an intramolecular disulfide bridge undergo characteristic loss of the elements of H2S2, a process diagnostic of the presence of the disulfide moeity. This facile process is initiated from a side-chain enolate anion. Theoretical calculations (at the HF/6-31G(d)//AM1 level of theory) indicate that the process is exothermic with a small barrier. When the disulfide link involves a C-terminal Cys, the negative ion spectrum shows an [(M--H)--(H2S2+CO2)] fragment anion which is usually the main peak of the spectrum. This process is also directed by an enolate anion: theoretical calculations suggest a stepwise sequence with loss of CO2 preceding loss of H2S2. Both [(M--H)--H2S2] and [(M--H)--(H2S2+CO2)] anions undergo backbone cleavage allowing identification of the amino acid sequence of the peptide.enAnimalsRana ridibundaPeptidesAntimicrobial Cationic PeptidesAmphibian ProteinsPeptide MappingSpectrometry, Mass, Electrospray IonizationAmino Acid SequenceMolecular Sequence DataJournal article002005118510.1002/rcm.21490002328666000122-s2.0-2754443659054516