title: The solid state oxidation of methionine containing peptide: a preliminary study using time of flight secondary ion mass spectrometry.
abstract: OBJECTIVE
  A surface sensitive mass spectrometric technique: Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) was introduced to study the solid state instability of a methionine containing peptide caused by the oxidation of the methionine residue.
  
  
  METHODS
  The oxidation of a neuropeptide Methinonine-Enkephalin (ME) in air and under UV acceleration was studied by ToF-SIMS.
  
  
  RESULTS
  The apparent oxidation rate is defined by the peak ratio of oxidized molecular ion over unoxidized molecular ion. ME is oxidized at a faster rate to its sulfoxide derivative in the UV accelerated oxidation environment than in lab air. The calibration curve for evaluating the ionization probability ratio of the oxidized deprotonated molecular ion divided by the unoxidized deprotonated molecular ion was obtained. This could be used to extract the real oxidation rate of ME in the solid state.
  
  
  CONCLUSIONS
  The preliminary results showed that ToF-SIMS with simple sample handling, fast data acquisition, together with excellent surface sensitivity and detection limit could be an applicable and convenient tool to study peptide reactions in the solid state such as oxidation and deamidation process.
authors.affiliation: Department of Chemistry, SUNY at Buffalo, New York 14260-3000, USA.
authors.forename: L
authors.initials: L
authors.lastname: Sun
authors.forename: J A
authors.initials: JA
authors.lastname: Gardella
mesh_terms: D004744:Enkephalin, Methionine / Q000737:chemistry*; D010084:Oxidation-Reduction; D018629:Spectrometry, Mass, Secondary Ion / Q000295:instrumentation / Q000379:methods
chemical_list: D004744:Enkephalin, Methionine