Proenkephalin-B(PDYN), belongs to the opioid neuropeptide precursor family. The N-terminal domain contains 6 conserved cysteines thought to be involved in disulfide bonding and/or processing. Leu-enkephalins, which is a type of Proenkephalin-B, compete 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. Dynorphin peptides differentially regulate the kappa opioid receptor. Dynorphin A has a typical opiod activity, it is 700 times more potent than Leu-enkephalin.