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 (PubMed:8624732). 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 (By similarity). Increases glutamate release in the striatum and decreases GABA concentration in the striatum. Increases glutamate release in the striatum. Expressed in brain, heart and testis. 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.