Cathepsin D: ProductsCathepsin D is a lysosomal aspartic protease of the pepsin family. Human Cathepsin D is synthesized as a precursor protein, consisting of a signal peptide (residues 1 - 18), a propeptide (residues 19 - 64), and a mature chain (residues 65 - 412). The mature chain can be processed further to the light (residues 65 - 161) and heavy (residues 169 - 412) chains. It is expressed in most cells and over expressed in breast cancer cells. Cathepsin D is a major enzyme in protein degradation in lysosomes, and also involved in the presentation of antigenic peptides. Mice deficient in Cathepsin D have been shown to develop a progressive atrophy of the intestinal mucosa, a massive destruction of lymphoid organs, and a profound neuronal ceroid lipofucinosis, indicating that Cathepsin D is essential for proteolysis of proteins regulating cell growth and tissue homeostasis. Cathepsin D secreted from human prostate carcinoma cells are responsible for the generation of angiostatin, a potent endogenous inhibitor of angiogenesis.