Carboxypeptidase (CP) A6 (CPA6, also known as CPAH; MEROPS identifier M14.018; ), belongs to the carboxypeptidase A/B subfamily of the M14 family of metallocarboxypeptidases (MCPs). The M14 family are zinc-binding CPs which hydrolyze single, C-terminal amino acids from polypeptide chains, and have a recognition site for the free C-terminal carboxyl group, which is a key determinant of specificity. CPA6 prefers large hydrophobic C-terminal amino acids as well as histidine, while peptides with a penultimate glycine or proline are very poorly cleaved.Several neuropeptides are processed by CPA6, including Met- and Leu-enkephalin, angiotensin I, and neurotensin. CPA6 converts enkephalin and neurotensin into forms known to be inactive toward their receptors, but converts inactive angiotensin I into the biologically active angiotensin II. Thus, CPA6 plays a possible role in the regulation of neuropeptides in the extracellular environment within the olfactory bulb where it is highly expressed []. It is also broadly expressed in embryonic tissue, being found in neuronal tissues, bone, skin as well as the lateral rectus eye muscle []. A disruption in the CPA6 gene is linked to Duane syndrome, a defect in the abducens nerve/lateral rectus muscle connection []. Mutations in the CPA6 gene have been identified in patients with epilepsy [].
