title: Investigation of non-covalent complexations of Ca(II) and Mg(II) ions with insulin by using electrospray ionization mass spectrometry.
abstract: BACKGROUND
  Insulin is a peptide hormone secreted by pancreatic β-cells. Ca(II) and Mg(II) ions play an important role in the secretion of insulin. There is no study about a direct complexation of Ca(II) or Mg(II) with insulin and their equilibrium constants. Electrospray ionization mass spectrometry (ESI-MS) is a practical method for the monitoring of non-covalent complexes such as Ca(II)-insulin and Mg(II)-insulin. Here, the equilibrium constants of Ca(II)-insulin and Mg(II)-insulin non-covalent complexes have been calculated after ESI-MS measurements in aqueous solutions.
  
  
  METHODS
  The effects of pH, competitive binding, ion exchange, and Na(I) and K(I) ions on Ca(II)-insulin and Mg(II)-insulin complexation have been examined by measuring by ESI-MS. The dissociation equilibrium constants (K1 and K2 ) of Ca(II)-insulin and Mg(II)-insulin complexes were calculated from the binomial graph derived from the ESI-MS normalized peak intensities. The MS/MS spectra of the complexes have been examined.
  
  
  RESULTS
  The dissociation equilibrium constants were found to K1 : 1.29 × 10(-4)  M and K2 : 9.69 × 10(-4)  M for the Ca(II)-insulin complexes, and K1 : 1.37 × 10(-4)  M and K2 : 9.12 × 10(-4)  M for Mg(II)-insulin complexes. Ca(II) ions have higher complexation capability with insulin than Mg(II) ions.
  
  
  CONCLUSIONS
  The binding equilibrium constants of Ca(II)- and Mg(II)-insulin non-covalent complexes have been determined successfully by ESI-MS. Ca(II) and Mg(II) ions are involved in the insulin secretion by forming non-covalent complexes. Copyright © 2016 John Wiley & Sons, Ltd.
authors.affiliation: Department of Chemistry, Faculty of Arts and Sciences, Sakarya University, 54187, Sakarya, Turkey.
authors.forename: Mustafa
authors.initials: M
authors.lastname: Gülfen
authors.affiliation: Department of Chemistry, Faculty of Arts and Sciences, Sakarya University, 54187, Sakarya, Turkey.
authors.forename: Abdil
authors.initials: A
authors.lastname: Özdemir
authors.affiliation: Genomics Research Center, Academia Sinica, Taipei, Taiwan.
authors.forename: Jung-Lee
authors.initials: JL
authors.lastname: Lin
authors.affiliation: Genomics Research Center, Academia Sinica, Taipei, Taiwan. winschen@gate.sinica.edu.tw.
authors.forename: Chung-Hsuan
authors.initials: CH
authors.lastname: Chen
mesh_terms: D002118:Calcium / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D008274:Magnesium / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D007328:Insulin; D008274:Magnesium; D002118:Calcium