Free Superoxide is an Intermediate in the Production of H2O2 by Copper(I)-A 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- (A) is found in AD brains, and Cu-A 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-A-catalyzed H2O2 production is however not known, although it was proposed that H2O2 is directly formed from O-2 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-A in the presence of ascorbate occurs mainly via a free O-2(.-) intermediate. This finding radically changes the view on the catalytic mechanism of H2O2 production by Cu-A, and opens the possibility that Cu-A-catalyzed O-2(.-) contributes to oxidative stress in AD, and hence may be of interest.