Endomorphin-2
Endomorphin-2 (EM-2) is an endogenous opioid peptide and one of the two endomorphins.[1] It has the amino acid sequence Tyr-Pro-Phe-Phe-NH2. It is a high affinity, highly selective agonist of the μ-opioid receptor, and along with endomorphin-1 (EM-1), has been proposed to be the actual endogenous ligand of this receptor (that is, rather than the endorphins).[1][2][3][4] Like EM-1, EM-2 produces analgesia in animals, but whereas EM-1 is more prevalent in the brain, EM-2 is more prevalent in the spinal cord.[1] In addition, the action of EM-2 differs from that of EM-1 somewhat, because EM-2 additionally induces the release of dynorphin A and [Met]enkephalin in the spinal cord and brain by an unknown mechanism, which in turn activate the κ- and δ-opioid receptors, respectively, and a portion of the analgesic effects of EM-2 is dependent on this action.[5][6] Moreover, while EM-1 produces conditioned place preference, a measure of drug reward, EM-2 produces conditioned place aversion, an effect which is dynorphin A-dependent.[6] Similarly to the case of EM-1, the gene encoding for EM-2 has not yet been identified.[4][7] See alsoReferences
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