Interaction between amyloid-β peptide and heme probed by electrochemistry and atomic force microscopy.

Heme binds to amyloid β-peptide (Aβ) in the brain of Alzheimer's disease (AD) patients, thus forming Aβ-heme complexes and leading the characteristic pathological features of AD. The interaction between heme and Aβ might have important biological relevance to AD etiology. In this work, the electrochemical performances of heme after incubation with Aβ1-42, Aβ fragments, and mutated Aβ were systematically investigated using cyclic voltammetry and differential pulse voltammetry. Our results indicated that His13 and His14 were possible binding sites, and Aβ bound two molecules of heme with a binding constant of K(a1) = 7.27 × 10(6) M(-1) (n(1) = 1.5) and K(a2) = 2.89 × 10(6) M(-1) (n(1) = 1.8). Detailed analysis with atomic force microscopy (AFM) of Aβ1-42 in the absence or presence of heme under the same incubation conditions showed that heme inhibited the formation of Aβ fibrils. According to results of the spectroscopic characterization, Arg5 was the key residue in making the heme-Aβ1-42 complex as a peroxidase.