ESI-MS measurements for the equilibrium constants of copper(II)-insulin complexes

The Role of Heme and Copper in Alzheimer's Disease and Type 2 Diabetes Mellitus

Beyond the well-explored proposition of protein aggregation or amyloidosis as the central event in amyloidogenic diseases like Alzheimer's Disease (AD), and Type 2 Diabetes Mellitus (T2Dm); there are alternative hypotheses, now becoming increasingly evident, which suggest that the small biomolecules like redox noninnocent metals (Fe, Cu, Zn, etc.) and cofactors (Heme) have a definite influence in the onset and extent of such degenerative maladies. Dyshomeostasis of these components remains as one of the common features in both AD and T2Dm etiology. Recent advances in this course reveal that the metal/cofactor-peptide interactions and covalent binding can alarmingly enhance and modify the toxic reactivities, oxidize vital biomolecules, significantly contribute to the oxidative stress leading to cell apoptosis, and may precede the amyloid fibrils formation by altering their native folds. This perspective highlights this aspect of amyloidogenic pathology which revolves around the impact of the metals and cofactors in the pathogenic courses of AD and T2Dm including the active site environments, altered reactivities, and the probable mechanisms involving some highly reactive intermediates as well. It also discusses some in vitro metal chelation or heme sequestration strategies which might serve as a possible remedy. These findings might open up a new paradigm in our conventional understanding of amyloidogenic diseases. Moreover, the interaction of the active sites with small molecules elucidates potential biochemical reactivities that can inspire designing of drug candidates for such pathologies.

Monitoring Silver(I)-Insulin Complexes with Electrospray Ionization Quadrupole Ion Trap Mass Spectrometry

Ag(I)-insulin complex formation was investigated using electrospray quadrupole ion trap mass spectrometry (ESI-QIT-MS), and Ag(I) ion binding to an insulin molecule was evaluated. The Ag(I) binding ratios were measured in the range of pH 3-8. The highest binding ratio of the Ag(I) ions was obtained at pH 7. Spectrometric titration was carried out at varied molar ratios of Ag(I) ions to insulin from 20/1 to 250/1. It was observed that four Ag(I) ions were bound effectively to an insulin molecule to form Ag(I)_1-4-insulin complexes. The formation equilibrium constants of Ag(I)_1-4-insulin complexes were calculated from the ESI-QIT-MS peak intensities. The equilibrium constants were found as K_f1 = (2.92 ± 0.18) × 10⁴ M^-1, K_f2 = (1.03 ± 0.07) × 10⁴ M^-1, K_f3 = (6.67 ± 0.46) × 10³ M^-1, and K_f4 = (2.00 ± 0.16) × 10³ M^-1. The tandem MS/MS spectroscopies were studied to evaluate the stability of the Ag(I) complexes. The different flow rates with nano-ESI were performed to determine the binding of Ag(I) ions in solution or gas phase. In conclusion, it was observed that the Ag(I) ion forms stable Ag(I)_1-4-complexes with high formation equilibrium constants.

Copper(ii) complexes with alloferon analogues containing phenylalanine H6F and H12F stability and biological activity lower stabilization of complexes compared to analogues containing tryptophan

Copper(ii) complex formation processes between alloferon 1 (Allo1) (H1 GVSGH6 GQH9 GVH12G) analogues where the phenylalanine residue is introduced in the place of His residue H6F and H12F have been studied by potentiometric, UV-visible, CD and EPR spectroscopic, and MS methods. For the phenylalanine analogues of alloferon 1, complex speciation has been obtained for a 1 : 1, 2 : 1 and 3 : 1 metal-to-ligand molar ratio. At physiological pH and in 1 : 1 metal-to-ligand molar ratio the phenylalanine analogues of alloferon 1 form a CuL complex similar to that of alanine analogues with the 4N{NH2,N1Im,2NIm} coordination mode. The stability of the complexes of the phenylalanine analogues is higher in comparison to those of alanine analogues, but lower in comparison to those containing tryptophan. Injection of Allo12F into insects induced prominent apoptotic changes in all hemocytes. The presence of apoptotic bodies only in the insect hemolymph testifies to the fact that Allo12F is an extremely pro-apoptotic peptide.