STRUCTURE

Endorphin Structure

1. Discovery
2. 3 types of endorphins
3. Similarity to morphine
4. Production of endorphins

DISCOVERY

Endorphins are the body's own natural pain killers, or "feel-good" drugs. Ever since their discovery, it seems that endorphins may behave like opiate drugs such as morphine and function as an internal mechanism for controlling pain sensations. Modern research hopes to develop a more natural substitute for morphine that is not addictive. The natural functions of endorphins have a wide range, covering everything from temperature to sense of well-being (13).


THREE TYPES OF ENDORPHINS

Endorphins are neuropeptides that can range from 2 to 39 amino acids in length. Neuropeptides are peptide molecules produced and released in the nervous system that act like transmitters (2). There are three different neuropeptide sequences including enkephalins, endorphins, and dynorphins. Each arises from its own gene (13). Two different structures exist for enkephalins. Although both consist of 5 amino acids, they differ in their terminal amino acid. One has methionine and the other has leucine. Endorphins are larger with 30 or more amino acids. Dynorphins are similar in structure to leu-enkephalin, but is much more potent and mediates more sedative actions at the cortical level.


SIMILARITY TO MORPHINE

The main purpose of endorphins is to depress activity in the cerebral cortex and thalamus. Endorphins have an amazing similarity to morphine (5). This was discovered upon the realization that particular parts of the brain have a high affinity for opiate drugs li`ine. These receptors were concentrated in areas of the brain and spinal cord that are involved with the perception and integration of pain (5). It has been found that there is an antagonist to morphine called naloxone. This drug blocks the binding of morphine to the opiate receptor. The structure of naloxone is such that it not only blocks stimulation- induced analgesia, but also blocks placebo analgesia (12). The similarity of morphine to endorphins is demonstrated by the fact that naloxone decreases the pain reducing effects (analgesia) of natural endorphins as well as morphine (5). Naloxone and morphine are quite similar in structure as
they both contain a number of benzene rings within the compound.


PRODUCTION OF ENDORPHINS

The naturally occurring endorphins are produced by pro-hormones. Beta-endorphin is made in the pituitary (11). Methionine and Leucine enkephalins are made in the chromaffin cells of the adrenal medulla (10). Pro-opiomelanocortin (POMC) is a precursor for beta lipotropin (6). The POMC gene is expressed in the pituitary and its products are released into the blood as a result of stress. Beta-lipotropin contains beta-endorphin and met-enkephalin (14). The beta-lipotropin will undergo hydrolysis by a trypsin-like enzyme to yield beta endorphin (B-End) (263). Pro-enkephalin will yield the two types of enkephalin molecules. Specifically, it will release 4 copies of the Met-enkephalin and one copy of the Leu-enkephalin. Pro-dynorphin results in the release of three copies of leu-enkephalin and a series of dynorphins. Dynorphin is an opioid tridecapeptide with an NH2 terminus resembling leu enkephalin. It is found in the pituitary, hypothalamus, and spinal cord (10).
The endorphins serve a very useful purpose in the body. They act in serious situations when you must act quickly to situations such as child birth. Their broad range of actions makes them an invaluable part of the human body.



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