Membrane-bound X-prolinyl aminopeptidase 2, also known as XPNPEP2, belongs to the M24B peptidase family. It has been reported that XPNPEP2 is associated with aminopeptidase P (APP) activity.The C-2399A variant of XPNPEP2 has been associated with reduced APP activity and increased incidence of AE-ACEi.APP is an N-terminal imide bond-specific hydrolase, and these bonds are common to several collagen degradation products, neuropeptides, vasoactive peptides, and cytokines.Membrane-bound and soluble forms of XPNPEP2 have been identified as 2 separate gene products. bound and soluble forms have been identified as 2 separate gene products. Translocation disrupts XPNPEP2, which encodes the Xaa proline aminopeptidase that hydrolyzes the N-terminal Xaa-proline bond. XPNPEP2 mRNA is detectable in fibroblasts undergoing translocation, suggesting that the gene at least partially escapes X chromosome inactivation.XPNPEP2 is a candidate gene for premature ovarian failure (POF).