Mechanism of hydrogen peroxide production by copper-bound amyloid beta peptide: a theoretical study.

The amyloid beta peptide (Abeta) of Alzheimer's disease evolves hydrogen peroxide in vitro in the presence of Cu(II), external reducing agents, and molecular oxygen, without producing detectable amounts of the one-electron reduced intermediate, superoxide, O(2)(-*). The mechanism of this process was examined by ab initio computational chemistry techniques in systems that model the binding of Cu(II) to the His13His14 fragment of Abeta. The catalytic cycle begins with the reduction of the most stable Cu(II) complex to the most stable Cu(I) complex. This Cu(I) complex forms a Cu(II)-like adduct with (3)O(2) that cannot dissociate in water to yield O(2)(-*). However, it can be reduced by proton-coupled electron transfer to an adduct between HOO(-) and the Cu(II)-like complex, which in turn can be protonated. The protonated complex decomposes to yield H(2)O(2) by an associative-dissociative mechanism, thus completing the cycle.