MetEnkephalin

Met-enkephalin, also known as methionine enkephalin, is an endogenous opioid peptide consisting of five amino acids: tyrosine–glycine–glycine–phenylalanine–methionine. It is derived from the larger precursor protein proenkephalin A and is found in the brain, spinal cord, adrenal gland, and other tissues.

Met-enkephalin functions as a natural analgesic by modulating nociceptive signaling in the central nervous system. It interacts with opioid receptors to influence pain perception, emotion, and stress responses. The peptide binds primarily to delta opioid receptors, with lesser affinity for mu receptors; activity at these receptors underpins its analgesic and modulatory effects.

The peptide is rapidly inactivated in the synaptic cleft by enkephalin-degrading enzymes, giving it a short physiological half-life. This rapid metabolism limits the effectiveness of Met-enkephalin when considered for therapeutic use as a drug, though it has informed the development of opioid peptides and receptor-targeted analgesics.

Met-enkephalin is one of several enkephalins derived from the PENK gene, which encodes proenkephalin A. Processing of this precursor yields multiple enkephalin peptides that contribute to the endogenous regulation of pain and affective states. Research on Met-enkephalin continues to explore its roles in pain, mood regulation, and potential therapeutic analogs with improved stability and receptor selectivity.