A member of the metalloproteinase family M16, nardilysin is most similar to insulin degrading enzyme, and the bacterial peptidase pitrilysin. It cleaves peptide substrates on the N terminus of arginine residues in dibasic pairs. Nardilysin was first described as a processing enzyme of somatostatin 1-28, which is cleaved at the Arg-Lys paired amino acid location. Nardilysin was named N arginine dibasic convertase (NRD convertase) to reflect this cleavage, although it was later shown that the activity was due to aminopeptidase B acting as a heterodimer with nardilysin. In addition to somatostatin 1-28, nardilysin cleaves dynorphin A and a-neoendorphin. Nardilysin was first detected in the brain and testis, and later in the heart, skeletal muscle, and in lesser amounts in most tissues and cell lines.