Cathepsin D is an enzyme found in many tissues throughout the body, primarily in lysosomes, which are cellular compartments responsible for breaking down waste materials. It plays a crucial role in protein degradation, helping to recycle cellular components and maintain cellular health. This enzyme is also involved in various biological processes, including immune response and tissue remodeling. Abnormal levels of Cathepsin D have been linked to several diseases, including certain types of cancer and neurodegenerative disorders, making it a subject of interest in medical research.