Enkephalin
From the Simple English Wikipedia, the free encyclopedia that anyone can change
Enkephalins were the first endorphins that were discovered in the brain. They are found in many parts of the brain, specially in the basal ganglia. They act as "natural pain killers".
Enkephalins are small proteins. They consist of five amino acids in each of their molecules. The last amino acid is either leucine (leu) or methionine (met).