Beta secretase is a protease responsible for the proteolytic processing of the amyloid precursor protein (APP). Amyloid beta peptide is the major constituent of amyloid plaques in the brains of individuals afflicted with Alzheimers disease. This peptide is generated from the beta-amyloid precursor protein (beta APP) in a two-step process. The first step involves cleavage of the extracellular, amino-terminal domain of beta APP. Protein cleavage is performed by an aspartyl protease termed beta-secretase (BACE), of which there are two isoforms, BACE1 and 2. Beta APP cleavage by beta-secretase results in the cellular secretion of a segment of beta APP and a membrane-bound remnant. This remnant is then processed by another protease termed gamma-secretase. Gamma-secretase cleaves an intra-membrane site in the carboxyl-terminal domain of beta APP, thus generating the amyloid beta peptide.