Exploring the reactions of b-Amyloid (Ab) peptide 1-28 with AlIII and FeIII ions

The reactions of human beta-amyloid peptide 1-28 (A beta 28) with Al-III and Fe-III ions were investigated by H-1 NMR and electrospray ionization mass spectrometry (ESI-MS) under pH conditions close to physiological ones. H-1 NMR titrations, performed in the 5.3-8.0 pH range, revealed that no measurable amounts of A beta 28-Al-III or A beta 28-Fe-III adducts are formed; such metal adducts could not be obtained even by changing a number of experimental conditions, e.g., temperature, buffer, nature of the salt, etc. These observations were later confirmed by ESI-MS. It is thus demonstrated that A beta 28, at physiological pH, is not able to form binary complexes with Al-III and Fe-III ions of sufficient stability to compete with metal hydroxide precipitation. The biological implications of these findings are discussed in the frame of current literature.