Effects of oxidation on redox and cytotoxic properties of copper complex of Aß1-16 peptide.

The effect of oxidation on redox and cytotoxic properties of copper complex of amyloid beta (Aß) peptide was studied by gamma radiolysis. The oxidation of Aß1-16 and Aß1-16/Cu(II) complex was carried out using hydroxyl ((•)OH) radicals produced by gamma radiolysis and the products were analyzed using mass spectrometry. The presence of Cu(II) was found to enhance the oxidation of Aß1-16 peptide. The oxidation of residues Asp1, His6, and His13 was enhanced due to their involvement in copper binding. The oxidation of His residues of Aß1-16 peptide, which are chiefly responsible for copper binding, resulted in altered redox properties and subsequently in higher cytotoxicity of the Aß1-16 peptide in SH-SY5Y cells.

Effects of oxidation on copper-binding properties of Aß1-16 peptide: a pulse radiolysis study.

The reaction of hydroxyl radicals ((•)OH) with Aß1-16 peptide was carried out using pulse radiolysis to understand the effect of oxidation of peptide on its copper-binding properties. This reaction produced oxidized, dimeric and trimeric Aß1-16 peptide species. The formation of these products was established with the help of fluorescence spectroscopy and mass spectrometry. The mass spectral data indicate that the major site of oxidation is at His6, while the site for dimerization is at Tyr10. Diethyl pyrocarbonate-treated Aß1-16 peptide did not produce any trimeric species upon oxidation with (•)OH. The quantitative chemical modification studies indicated that one of the three histidine residues is covalently modified during pulse radiolysis. The copper-binding studies of the oxidized peptide revealed that it has similar copper-binding properties as the unoxidized peptide. Further, the cytotoxicity studies point out that both oxidized and unoxidized Aß1-16 peptide are equally efficient in producing free radicals in presence of copper and ascorbate that resulted in comparable cell death.