XPNPEP1 is a proline-specific metalloaminopeptidase that specifically catalyzes the removal of any unsubstituted N-terminal amino acid that is adjacent to a penultimate proline residue. As a result of its specificity toward proline, it has been suggested that XPNPEP1 is important in the maturation and degradation of peptide hormones, neuropeptides, and tachykinins, as well as in the digestion of otherwise resistant dietary protein fragments, thereby complementing the pancreatic peptidases. Deficiency of XPNPEP1 results in excretion of large amounts of imino-oligopeptides in urine.
