title: Formation of deaminated dimer species of amino acids by atmospheric pressure chemical ionization.
abstract: BACKGROUND
  Interactions of biological molecules to form cluster species play a key role in biological processes and investigation of non-covalent complexes is one of the research fields using mass spectrometry. Atmospheric pressure chemical ionization mass spectrometry (APCI-MS) is a useful method for the investigation of cluster formation of amino acids (AAs) by ion-molecule reactions.
  
  
  METHODS
  A mixture of 20 protein AAs was ionized by APCI and the product ions were analyzed. The ionization was performed in the positive and negative ion modes. Formation of the homo- and heterocluster ions of AAs was investigated. Mechanism for the formation of AA homo- and heterocluster ions was examined using hydrogen/deuterium (H/D)-exchange experiments.
  
  
  RESULTS
  In the positive ion mode, of the dimer species only the [2Pro+H](+) ion was detected. In the negative ion mode, the [2M - H](-) ions of His, Val, Ser, and Gln were observed. The deaminated dimers such as the [2Gln - H - NH3](-) and [His + Gln - H - NH3](-) ions were also observed. In the negative ion mass spectra of the His/Arg, His/Asn, and His/Lys binary mixture solutions, the [His + AA - H - NH3](-) ions of Asn, Arg, and Lys were also detected.
  
  
  CONCLUSIONS
  The number and abundances of the negative product ions were much greater than those of the positive ones. Mechanism for the formation of [2Gln - H - NH3](-) and [His+AA - H - NH3](-) was examined by deuterium replacement of the amine and hydroxide groups to distinguish the deamination and dehydration reactions with a single quadrupole mass spectrometer. The [His + AA - H - NH3](-) ion is formed by ion-molecule reaction between the [His-H](-) ion and a neutral AA.
authors.affiliation: Department of Chemistry, Sejong University, 98 Gunja-dong, Gwangjin-gu, Seoul, 143-747, Korea.
authors.forename: Sung-Seen
authors.initials: SS
authors.lastname: Choi
authors.forename: Ok-Bae
authors.initials: OB
authors.lastname: Kim
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D001274:Atmospheric Pressure; D003903:Deuterium; D007477:Ions / Q000737:chemistry; D013058:Mass Spectrometry / Q000379:methods*
chemical_list: D000596:Amino Acids; D007477:Ions; D003903:Deuterium