Amyloid precursor protein (APP(18-770)) is processed by one of two distinct proteolytic pathways; the non-amyloidogenic pathway where alpha-secretase cleaves APP at the cell surface within the A-beta domain, liberating APPs-alpha and the amyloidogenic pathway, where beta-secretase followed by gamma-secretase cleavages results in peptides which are the main fibril-forming peptides implicated in Alzheimer's disease. In the first step of the amyloidogenic pathway, the endosomal membrane protein beta-secretase 1 (BACE1) catalyses the cleavage of APP(18-770) within the ectodomain and liberates a soluble proteolytic fragment, termed soluble APP-beta (APPs-beta, APP(18-671)) and C99 (APP(672-770) (Baranello et al. 2015, Andrew et al. 2016). APP processing can occur in several endocytic and secretory pathways. For simplicity, the endosome has been chosen in this event.