[Leu5]-Enkephalin is an endogenous opioid peptide neurotransmitter that is found in the brains of many animals including humans. [Leu5]-Enkephalin is one of the two forms of enkephalin, the other being met-enkephalin. The tyrosine residue at position 1 is analogous to the 3-hydroxyl group on morphine and [Leu5]-enkephalin acts as an agonist at both µ- and delta-opioid receptors, with greater preference for delta and little to no effect on the kappa -opioid receptor.
