Quantifying Na(I)-insulin and K(I)-insulin non-covalent complexes by ESI-MS method and calculation of their equilibrium constants

Abstract

In this study, the dissociation and formation equilibrium constants of Na(l)-insulin and K(I)-insulin complexes have been calculated after the quantifying them on ESI mass spectrometer. The ESI-MS spectra of the complexes were measured by using the solvents as 50% MeOH in water and 100% water. The effect of pH on the Na(I)-insulin and K(I)-insulin complex formation were examined. Serial binding of Na(I) and K(I) ions to the insulin molecule were observed in the ESI-MS measurements. The first formation equilibrium constants were calculated as K-f1 : 5.48 x 10(3) 1/M for Na(l)-insulin complex and K-f1: 4.87 x 10(3) 1/M for K(I)-insulin in water. The binding capability of Na(l) ions to insulin molecule is higher than the capability of K(I) ions. In case of a comparison together with Ca(II)-insulin and Mg(II)-insulin, the formation equilibrium constants (K-f1) are in order of Ca(II)-insulin > Mg(II)-insulin > Na(l)-insulin > K(I)-insulin in water. The results showed that Na(l) and K(I) ions are involved in the formation of the non-covalent complexes with insulin molecule, since high extracellular and intracellular concentrations of them in the body. (C) 2017 Elsevier B.V. All rights reserved.