enkephalin

n. natural chemical having opiate characteristics that is secreted in the brain and spinal cord and acts as painkiller (Biochemistry)

An enkephalin is a pentapeptide ending with either leucine ("leu") or methionine ("met"). Both are products of the proenkephalin gene. Met-enkephalin is Tyr-Gly-Gly-Phe-Met. Leu-enkephalin has Tyr-Gly-Gly-Phe-Leu.Enkephalins play many roles in regulating pain.
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Enkephalin /en·keph·a·lin/ either of two pentapeptides occurring in the brain and spinal cord and also in the gastrointestinal tract; they have [more]Enkephalin - Community and Resources

Noun
1. an endorphin having opiate qualities that occurs in the brain and spinal cord and elsewhere
(hypernym) endorphin

Enkephalins are molecules produced naturally by the central nervous system to numb pain. Enkephalins lock into receptors on the surface of a nerve cell and open ion channels. Ions flow into the cell and the distribution of charge on either side of the cell membrane becomes such that the nerve cell cannot fire.