Α-Endorphin

Relation to beta- and gamma-endorphin

Endorphins are generally known as neurotransmitters that are released when the body goes into pain. The three endorphins that play a role in this response are α-endorphin, β-endorphin (beta-endorphin), and γ-endorphin (gamma-endorphin) which are all derived from the same polypeptide known as pro-opiomelanocortin. Although all play roles as neurotransmitters, the specific effects of all three differ. The most studied endorphin of the three is β-endorphin. α-Endorphins are known to contain one less amino acid than γ-endorphins, differing by a single leucine amino acid at the terminal end. Although this may seem minor, It allows them to have vastly different effects. Studies found that γ-endorphins and α-endorphins have opposite effects which allow them to help maintain a level of homeostasis within the brain and behavior of animals. All of the specific effects on the body of α-endorphins are not yet fully studied nor fully understood by the science community. However, some studies suggest that these endorphins behave similarly to amphetamines. Similarly, other studies agree that Alpha-endorphins effects are similar to psychostimulant drugs.

Ranking based length, α-endorphins are the shortest with 16 amino acid residues. Meanwhile, the β-endorphin has the longest chain which begins with the same 16 amino acids as α-Endorphins: Tyr-Gly-Gly-Phe-Met-Thr-Ser-Glu-Lys-Ser-Gln-Thr-Pro-Leu-Val-Thr. The same sequence is also present in γ-endorphin. The beginning Tyr-Gly-Gly-Phe-Met chain is also known as the N-terminal pentapeptide opioid sequence. With such configuration, endorphins act as agonists to opioid receptors in the brain.

Effects on behavior

Studies have shown that α-endorphin is the strongest peptide in delaying avoidance behaviors. α-Endorphin has the same C-terminal sequence of β-LPH, allowing these peptides to have a high affinity for opiate binding sites. Even a slight difference in the C-terminal amino acid can have drastic effects on avoidance behavior. The importance in sequencing determines the function of the endorphin. When an N-terminal amino acid such as tyrosine is removed, there seems to be no significant impacts on avoidance behavior. However, when there are adjustments to the C-terminal sequence, like removing β-LPH 61-65; activity of the endorphin decreases.

References

References

1. (September 1979). "Specific nonopiate receptors for beta-endorphin". Science.
2. (November 1976). "Isolation, primary structure, and synthesis of a-endorphin and g-endorphin, two peptides of hypothalamic-hypophysial origin with morphinomimetic activity". Proceedings of the National Academy of Sciences.
3. (1977). "The expanding significance of hypothalamic peptides, or, is endocrinology a branch of neuroendocrinology?". Elsevier.
4. (October 1982). "Behavioral effects of neuropeptides: endorphins and vasopressin". Annual Review of Physiology.
5. (1992). "Endorphins and schizophrenia".
6. (January 1980). "Selective conversion of beta-endorphin into peptides related to gamma- and alpha-endorphin". Nature.
7. (2021). "StatPearls". StatPearls Publishing.
8. (1981-01-01). "Endocrinology, Neuroendocrinology, Neuropeptides". Pergamon.