Free superoxide is an intermediate in the production of H₂O₂ by copper(I)-Aβ peptide and O₂

Oxidative stress is considered as an important factor and an early event in the etiology of Alzheimer's disease (AD). Cu bound to the peptide amyloid-β (Aβ) is found in AD brains, and Cu-Aβ could contribute to this oxidative stress, as it is able to produce in vitro H₂O₂ and HO^. in the presence of oxygen and biological reducing agents such as ascorbate. The mechanism of Cu-Aβ-catalyzed H₂O₂ production is however not known, although it was proposed that H₂O₂ is directly formed from O₂ via a 2-electron process. Here, we implement an electrochemical setup and use the specificity of superoxide dismutase-1 (SOD1) to show, for the first time, that H₂O₂ production by Cu-Aβ in the presence of ascorbate occurs mainly via a free O₂^.- intermediate. This finding radically changes the view on the catalytic mechanism of H₂O₂ production by Cu-Aβ, and opens the possibility that Cu-Aβ-catalyzed O₂^.- contributes to oxidative stress in AD, and hence may be of interest. Cause of stress: Mechanistic studies reveal that copper-amyloid-β reduces dioxygen and produces predominantly superoxide as an intermediate for H₂O₂ formation. This finding implies that Cu-Aβ-catalyzed O₂^.- formation could contribute to oxidative stress in Alzheimer's disease.