A Direct Determination of the Dissociation Constant for the Cu(II) Complex of Amyloid β 1-40 Peptide

Interactions of amyloid β (Aβ) peptides with Cu(II) are believed to play a crucial role in the molecular mechanisms of neurotoxicity of Alzheimer’s disease. There is, however, a serious disagreement regarding the strength of Cu(II) binding to these peptides. We used recombinant amyloid β peptide 1−40 (Aβ40) to determine the stoichiometry and dissociation constants of Cu(II)−Aβ40 complexes using fluorescence spectroscopy. A single Cu(Aβ40) complex, characterized with the conditional dissociation constant Kdcond = 57 ± 5 nM was identified. This complex does not bind Hepes buffer molecules, as indicated by the total lack of relationship between Kdcond values and Hepes concentration. The differences between this and other determinations of this constant and its relevance for the understanding of Cu(II) interaction with Aβ peptides are discussed.