title: Photolytic determination of charge state for large proteins and fragments in an ion trap mass spectrometer.
abstract: BACKGROUND
  One of the major shortcomings of linear ion trap mass spectrometers is poor resolution. Failure to resolve isotopic peaks makes charge state determination for large proteins very difficult, hindering the ability to perform top-down proteomics.
  
  
  METHODS
  Peptides, proteins and corresponding fragments modified with para-iodobenzoate were trapped and irradiated with 266 nm light from an Nd:YAG laser. Loss of iodine due to photodissociation was then used to assign charge states by measuring the corresponding m/z shifts.
  
  
  RESULTS
  Initial experiments on small peptides illustrate the feasibility of the method. Further studies performed on larger proteins in higher charge states yielded similar results, revealing that fragment ions over a significant mass range either remain in or are quickly cooled to the laser overlap region of the ion trap.
  
  
  CONCLUSIONS
  Rapid charge state assignment for both whole molecules and collision-induced dissociation (CID) fragments can be obtained by photoactivation of chromophores with labile carbon-iodine bonds.
authors.affiliation: Department of Chemistry, University of California, Riverside, 501 Big Springs Road, Riverside, CA, 92521, USA.
authors.forename: Yana A
authors.initials: YA
authors.lastname: Lyon
authors.affiliation: Department of Chemistry, University of California, Riverside, 501 Big Springs Road, Riverside, CA, 92521, USA.
authors.forename: Ryan R
authors.initials: RR
authors.lastname: Julian
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D045304:Cytochromes c / Q000737:chemistry*; D054879:Halogenation; D006736:Horses; D007463:Iodobenzoates / Q000737:chemistry; D013058:Mass Spectrometry / Q000379:methods; D009211:Myoglobin / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry*; D010782:Photolysis; D055672:Static Electricity
chemical_list: D007463:Iodobenzoates; D009211:Myoglobin; D010455:Peptides; D045304:Cytochromes c