 It is also present in the periphery, notably in some primary afferent fibers that innervate the pelvic viscera.Met-enkephalin is synthesized from proenkephalin via proteolytic cleavage in two metabolic steps.Proenkephalin A is first reduced by either one of two trypsin-like endopeptidase enzymes, prohormone convertase 1 (PC1) or prohormone convertase 2 (PC2); then, the resulting intermediates are further reduced by the enzyme carboxypeptidase E (CPE; previously known as enkephalin convertase (EC)).