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. Met-enkephalin-Arg-Phe neuropeptide acts as a strong ligand of Mu-type opioid receptor OPRM1. Met-enkephalin-Arg-Phe-binding to OPRM1 in the nucleus accumbens of the brain increases activation of OPRM1, leading to long-term synaptic depression of glutamate release. Increases glutamate release in the striatum and decreases GABA concentration in the striatum. Increases glutamate release in the striatum. Proenkephalin-A is cleaved by CTSL to generate Met-enkephalin. Processed and degraded by ACE. Processed and degraded by ACE. Probably cleaved by ACE. Processed by ACE to generate Met-enkephalin in the nucleus accumbens of the brain. The N-terminal domain contains 6 conserved cysteines thought to be involved in disulfide bonding and/or processing. Belongs to the opioid neuropeptide precursor family.