Investigation of manganese(II)-insulin complexes using electrospray ionization mass spectrometry

Abstract

Manganese is a trace element in human nutrition. It is involved in many enzymes, proteins and biological activities. Mn(II) ion has the capable of binding to protein or peptides. Insulin is a blood glucose-lowering peptide hormone and it is secreted by the pancreatic (beta-cells. In this study, the binding capability of Mn(II) ions to insulin was studied using ESI-MS, nano-ESI-MS and MS/MS methods. The binding of Mn(II) ions to insulin molecule was studied by examining the effect of pH, the molar ratio of Mn(II) ions to insulin, the flow rate with nano-ESI system and MS/MS spectrometry. The ESI-MS measurements showed that the Mn(II)-insulin complexation mostly produces ML and M2L type complexes. The highest binding ratio was found at pH 7. The complex formation equilibrium constants of Mn(II)-insulin were calculated as k(f1): 1.03 +/- 0.12 x 10(4) and K-f2: 1.93 +/- 0.17 x 10(3). The nano-ESI-MS and MS/MS measurements exhibited strong and specific binding of Mn(II) ions to insulin molecule. It was concluded from all the ESI-MS measurements that Mn(II) ion has a high affinity to insulin molecule to form stable complexes. (C) 2018 Elsevier B.V. All rights reserved.