Aminopeptidase N is located in the small-intestinal and
renal microvillar membrane, and also in other plasma membranes. In
the small intestine aminopeptidase N plays a role in the final
digestion of peptides generated from hydrolysis of proteins by
gastric and pancreatic proteases. Its function in proximal tubular
epithelial cells and other cell types is less clear. The large
extracellular carboxyterminal domain contains a pentapeptide
consensus sequence characteristic of members of the zinc-binding
metalloproteinase superfamily. Sequence comparisons with known
enzymes of this class showed that CD13 and aminopeptidase N are
identical. The latter enzyme was thought to be involved in the
metabolism of regulatory peptides by diverse cell types, including
small intestinal and renal tubular epithelial cells, macrophages,
granulocytes, and synaptic membranes from the CNS. Human
aminopeptidase N is a receptor for one strain of human coronavirus
that is an important cause of upper respiratory tract infections.
Defects in this gene appear to be a cause of various types of
leukemia or lymphoma.
