title: Investigation of non-covalent complexes of glutathione with common amino acids by electrospray ionization mass spectrometry.
abstract: OBJECTIVE
  To study the non-covalent interaction between glutathione and common amino acids.
  
  
  METHODS
  A stoichiometry of glutathione and common amino acids were mixed to reach the equilibrium, and then the mixed solution was investigated by electrospray ionization mass spectrometry (ESI-MS). The binding of the complexes was further examined by collision-induced dissociation (CID) in a tandem mass spectrometer as well as UV spectroscopy. To avoid distinct ionization efficiency discrepancy and signal suppression in the ESI-MS measurements, the interaction between glutathione (GSH) and glutamate (Glu) was quantitatively evaluated. The total concentrations and series of m/z of peak intensities for glutathione and amino acids could be achieved, respectively. Due to the existence of some oligomeric species arising from glutathione or amino acids, an improved calculation formula was proposed to calculate the dissociation constants of glutathione binding to amino acids.
  
  
  RESULTS
  The ESI mass spectra revealed that glutathione could interact easily with Met, Phe, Tyr, Ser, or Ile to form non-covalent complexes. The binding of the complexes was further confirmed by CID experiments in a tandem mass spectrometer as well as UV spectroscopy. Moreover, an improved calculation formula was successfully applied to determine the dissociation constants of glutathione binding to Glu, His, or Gln. Finally, a possible formation mechanism for the complexes of glutathione with amino acids was proposed.
  
  
  CONCLUSIONS
  The reduced polypeptide gamma-glutathione can interact with each of 8 common amino acids, including Glu, His, and Gln to form non-covalent complexes with different affinity.
authors.affiliation: Department of Infectious Disease, Huadong Hospital, Shanghai 200040, China.
authors.forename: Zhao-yun
authors.initials: ZY
authors.lastname: Dai
authors.forename: Yan-qiu
authors.initials: YQ
authors.lastname: Chu
authors.forename: Bo
authors.initials: B
authors.lastname: Wu
authors.forename: Liang
authors.initials: L
authors.lastname: Wu
authors.forename: Chuan-fan
authors.initials: CF
authors.lastname: Ding
mesh_terms: D000465:Algorithms; D000596:Amino Acids / Q000737:chemistry*; D005947:Glucose / Q000737:chemistry; D005978:Glutathione / Q000737:chemistry*; D016014:Linear Models; D021241:Spectrometry, Mass, Electrospray Ionization; D013056:Spectrophotometry, Ultraviolet
chemical_list: D000596:Amino Acids; D005978:Glutathione; D005947:Glucose