In addition, there are 4 other mammalian enzymes named CPA-3 through CPA-6, and none of these are expressed in the pancreas.  Instead, these other CPA-like enzymes have diverse functions. 
* CPA3 (also known as mast-cell CPA) is involved in the digestion of proteins by mast cells.
* CPA4 (previously known as CPA-3, but renumbered when mast-cell CPA was designated CPA-3) may be involved in tumor progression, but this enzyme has not been well studied.
* CPA5 has not been well studied.
* CPA6 is expressed in many tissues during mouse development, and in adult shows a more limited distribution in brain and several other tissues. CPA6 is present in the extracellular matrix where it is enzymatically active.  A human mutation of CPA-6 has been linked to Duane's syndrome (abnormal eye movement).  Recently, mutations in CPA6 were found to be linked to epilepsy. CPA6 is also one of several enzymes which degrade enkephalins.