Electrochemical investigation on the complexes of Cu(II), Mn(II), Ca(II), and Mg(II) with insulin

Biological metal ions play crucial roles in various life processes and exhibit diverse biological functions. Specifically, Ca(II), Mg(II), Cu(II), and Mn (II) ions are intricately involved in insulin function. To further clarify the biological functions of biological metal ions on insulin, the interaction mechanism of insulin affected by Ca(II), Mg(II), Cu(II), and Mn (II) ions were comparably investigated via spectroscopic, circular dichroism(CD), and electrochemical approaches. Electrochemical studies demonstrate that Mn(II) forms an M2L-type complex with insulin, exhibiting a binding constant of beta Mn = 9.3 x 109, while Cu(II) and insulin form an M4L-type complex with a significantly higher binding constant of beta Cu=9.18 x 1012. Electrochemical investigation of the interaction between Ca(II) and Mg(II) with insulin adsorbed onto a glass carbon electrode surface revealed that the presence of Ca(II) and Mg(II) induced conformational changes in insulin, resulting in reduced adsorption capacity. Additionally, it was observed that the presence of Ca(II) and Mg(II) enhanced the redox signal of probe ions. The binding constants values were calculated to be 1.108 x 103 L center dot mol-1 for the insulin-Ca(II) system and 2.28 x102 L center dot mol-1 for the insulin-Mg(II) system. Spectroscopic studies showed that the binding of Cu(II) ions to insulin molecules may be controlled by chelation mechanism, and the interaction between Cu(II) ions and insulin molecules may occur in the aromatic region. Mn(II) ion binding is mainly controlled by ionic interactions, and its binding site is far away from the aromatic region.The combination of Ca(II) and Mg(II) with insulin induced a small enhancement in the Ultraviolet-visible (UV) absorption peak, with Ca(II) exhibiting a more pronounced effect compared to Mg(II). The results of spectral, CD and electrochemical studies are consistent.