Peptidase family M13 includes neprilysin, endothelin-converting enzyme IM13 family of metallopeptidases includes neprilysin (neutral endopeptidase, NEP, enkephalinase, CD10, CALLA, EC 220.127.116.11), endothelin-converting enzyme I (ECE-1, EC 18.104.22.168), erythrocyte surface antigen KELL (ECE-3), phosphate-regulating gene on the X chromosome (PHEX), soluble secreted endopeptidase (SEP), and damage-induced neuronal endopeptidase (DINE)/X-converting enzyme (XCE). These proteins consist of a short N-terminal cytoplasmic domain, a single transmembrane helix, and a larger C-terminal extracellular domain containing the active site. Proteins in this family fulfill a broad range of physiological roles due to the greater variation in the S2' subsite allowing substrate specificity. NEP is expressed in a variety of tissues including kidney and brain, and is involved in many physiological and pathological processes, including blood pressure and inflammatory response. It degrades a wide array of substrates such as substance P, enkephalins, cholecystokinin, neurotensin and somatostatin. It is an important enzyme in the regulation of amyloid-beta (Abeta) protein that forms amyloid plaques that are associated with Alzeimers disease (AD). ECE-1 catalyzes the final rate-limiting step in the biosynthesis of endothelins via post-translational conversion of the biologically inactive big endothelins. Like NEP, it also hydrolyses bradykinin, substance P, neurotensin and Abeta. Endothelin-1 overproduction has been implicated in various diseases, including stroke, asthma, hypertension, and cardiac and renal failure. Kell is a homolog of NEP and constitutes a major antigen on human erythrocytes; it preferentially cleaves big endothelin-3 to produce bioactive endothelin-3, but is also known to cleave substance P and neurokinin A. PHEX forms a complex interaction with fibroblast growth factor 23 (FGF23) and matrix extracellular phosphoglycoprotein, causing bone mineralization. A loss-of-function mutation in PHEX disrupts this interaction leading to hypophosphatemic rickets; X-linked hypophosphatemic (XLH) rickets is the most common form of metabolic rickets. ECEL1 is a brain metalloprotease involved in the critical role in the nervous regulation of the respiratory system, while DINE (damage induced neuronal endopeptidase) is abundantly expressed in the hypothalamus and its expression responds to nerve injury as well. Thus, majority of these M13 proteases are prime therapeutic targets for selective inhibition.