Experimental evidence increasingly implicates the beta-amyloid peptide in the pathogenesis of Alzheimer's disease. Beta-amyloid filaments dramatically accumulate in the neuritic plaques and vascular deposits as the result of the brain's inability to clear these structures. In this paper, we demonstrate that in addition to the intrinsic stability of A beta N-42, the time dependent generation of irreversibly associated A beta dimers and tetramers incorporated into A beta filaments are themselves resistant to proteolytic degradation. The presence of post-translational modifications such as isomerization of aspartyls 1 and 7, cyclization of glutamyl 3 to pyroglutamyl and oxidation of methionyl 35, further contribute to the insolubility and stability of A beta. All these factors promote the accumulation of neurotoxic amyloid in the brains of patients with Alzheimer's disease, and should be considered in therapeutic strategies directed towards the dissociation of the brain's A beta filaments.
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