Binding of Zn(II), Cu(II), and Fe(II) ions to alzheimerʹs Aß peptide studied by fluorescence

Binding of Zn(II), Cu(II) and Fe(II) ions to Aβ1-40, Aβ1-42 and a single tryptophan mutant of Aβ1-40 in solution at pH 7.4 was studied by fluorescent titration. Job plots and fitting of titration curves revealed formation of 1:1 and 1:2 peptide-metal complexes. For dimeric peptides Aβ1-40 and AβF4W the order of metal to peptide affinities is Fe < Cu > Zn, which is in agreement with the Irving-Williams series of complex stability. The affinity of Aβ1-42 for Fe increases dramatically upon aggregation: K changes from ca. 100 to ca. 0.2 μM.