Leu-enkephalin

Leu-enkephalin is an endogenous opioid peptide neurotransmitter found naturally in the brains of many animals, including humans. It is one of the two forms of enkephalin; the other is met-enkephalin. The tyrosine residue at position 1 is thought to be analogous to the 3-hydroxyl group on morphine.

Leu-Enkephalin is a peptide whose sequence is: Tyr - Gly - Gly - Phe - Leu. It produces pharmacological effects at both the mu and delta opioid receptors, showing selectivity for the delta receptor.

It has a much higher selectivity for δ opioid receptors than μ receptors, and has little to no effect on κ opioid receptors.

Leu-enkefalin