Beta-amyloid protein (A beta), a 39-43 amino acid peptide composed of a portion of the transmembrane domain and the extracellular domain of the amyloid precursor protein (APP), is also the principal component of amyloid. Research found that amyloid beta-protein circulates in human blood and in cerebrospinal fluid and is deposited into plaques found in the brains of patients with Alzheimer's disease (AD). The aggregation of the beta-amyloid protein into dense plaques on the exterior of brain cells results in destroys of the synapses and conduction of nerve impulses.
References:
1. Sisodia SS, Price DL. Role of the beta-amyloid protein in Alzheimer's disease. FASEB J. 1995 Mar; 9(5): 366-70..