An
enkephalin is a
pentapeptide involved in regulating
nociception in the body. The enkephalins are termed endogenous
ligands, as they are internally derived and bind to the body's opioid receptors. Discovered in 1975, two forms of enkephalin were revealed, one containing
leucine ("leu"), and the other containing
methionine ("met"). Both are products of the proenkephalin gene.