Neuropeptide that competes with and mimic the effects of opiate drugs. They play a role in a number of physiologic functions, including pain perception and responses to stress. Neuropeptide that competes with and mimic the effects of opiate drugs. They play a role in a number of physiologic functions, including pain perception and responses to stress. Processed and degraded by ACE. Processed and degraded by ACE. The N-terminal domain contains 6 conserved cysteines thought to be involved in disulfide bonding and/or processing. Proenkephalin-A is cleaved by CTSL to generate Met-enkephalin. Belongs to the opioid neuropeptide precursor family.