Amyloid precursor protein (APP) cleavage, animation. APP (blue) is shown with two enzyme molecules: gamma and beta secretase (purple). At centre, the enzymes have bound to APP, causing the molecule to separate into four fragments, one of which moves from the membrane to the foreground. It is this fragment that is the beta amyloid peptide that is implicated in conditions such as Alzheimer's disease. APP is a complex protein with many functions. It is found on the surface of cells throughout the body.