Investigation of non‐covalent complexations of Ca(II) and Mg(II) ions with insulin by using electrospray ionization mass spectrometry. (5th September 2016) - Gülfen, Mustafa
Abstract : Rationale: 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 ( K 1 and K 2 ) 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 K 1 : 1.29 × 10 −4 M and K 2 : 9.69 × 10 −4 M for the Ca(II)‐insulin complexes, and K 1 : 1.37 × 10 −4 M and K 2 : 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.