Aβ(1-40) Y10F, where the tyrosine moiety is substituted by phenylalanine (Phe, F)). Oxidation of tyrosine leads to the formation of stable dityrosine dimers of Aβs, whose importance is widely discussed in the pathogenesis of AD. According to Enache and Oliveira-Brett, in the initial step of oxidation, Tyr undergoes a one-electron and one-proton transfer to form the tyrosine phenoxyl radical (Tyr • ). This is a pH-dependent process, occurring at a potential ~ 0.65 V vs.