Presenilin-1 (PS-1) and Presenilin-2 (PS-2) are integral membrane proteins that contain multiple transmembrane domains. Both are predominantly located within the endoplasmic reticulum (ER) and early Golgi apparatus. They are primarily expressed in neurons and are ubiquitously expressed in the brain. PS-1 and PS-2 are proteolytically cleaved to generate an N-terminal fragment (NTF) and a C-terminal fragment (CTF). Mutations in the gene for Presenilin may play an important role in the pathology of Alzheimer's disease.