In the brains of patients with Alzheimer's disease, amyloid composed of 4kD amyloid beta protein is deposited in senile plaques and in blood vessel walls. Amyloid beta protein is a 39-43aa polypeptide with heterogeneous termini that is generated from the cleavage of a larger amyloid precursor protein (APP), which under appropriate cellular conditions, aggregate as senile plaques, which is a critical step in the neurodegenerative processes associated with AD. Cleavgae of the transmembrane region of APP by