CPE facilitates POMC transport into immature budding vesicles.
![β-endorphin β-endorphin](https://syntides.com/wp-content/uploads/2017/02/Product-Photo.png)
At the trans-Golgi network, POMC binds to a membrane-bound protein, carboxypeptidase E (CPE). All three types of endorphins are fragments of the precursor protein proopiomelanocortin (POMC). Tyr-Gly-Gly-Phe-Met-Thr-Ser-Glu-Lys-Ser-Gln-Thr-Pro-Leu-Val-Thr-Leu-OHĮndorphin precursors are primarily produced in the pituitary gland. Tyr-Gly-Gly-Phe-Met-Thr-Ser-Glu-Lys-Ser-Gln-Thr-Pro-Leu-Val-Thr-Leu-Phe-Lys-Asn-Ala-Ile-Ile-Lys-Asn-Ala-Tyr-Lys-Lys-Gly-Glu Tyr-Gly-Gly-Phe-Met-Thr-Ser-Glu-Lys-Ser-Gln-Thr-Pro-Leu-Val-Thr-OH Some studies have characterized α-endorphin activity as similar to that of psychostimulants and γ-endorphin activity to that neuroleptics separately. While β-endorphin is studied for its opioid activity, α-endorphin and γ-endorphin both lack affinity for opiate receptors and thus do not affect the body in the same way that β-endorphin does. Α-endorphin and γ-endorphin are primarily found in the anterior and intermediate pituitary. α-endorphin has the shortest sequence, and β-endorphin has the longest sequence. α-endorphin and γ-endorphin result from proteolytic cleavage of β-endorphin between the Thr(16)-Leu(17) residues and Leu(17)-Phe(18) respectively. The endorphins are all synthesized from the precursor protein, proopiomelanocortin, and all contain a Met-enkephalin motif at their N-terminus: Tyr-Gly-Gly-Phe-Met. The class of endorphins consists of three endogenous opioid peptides: α-endorphin, β-endorphin, and γ-endorphin. Thus, endorphin is a contraction of 'endo(genous) (mo)rphin' (morphin being the old spelling of morphine). The word endorphin is derived from ἔνδον / Greek: éndon meaning "within" ( endogenous, ἐνδογενής / Greek: endogenes, "proceeding from within"), and morphine, from Morpheus ( Ancient Greek: Μορφεύς, romanized: Morpheús), the god of dreams in the Greek mythology. Opioid peptides are classified based on their precursor propeptide: all endorphins are synthesized from the precursor proopiomelanocortin (POMC), encoded by proenkephalin A, and dynorphins encoded by pre-dynorphin. Studies have subsequently distinguished between enkephalins, endorphins, and endogenously-produced morphine, which is not a peptide. In addition, they found that it is completely removed from opiate receptors by naloxone, an identified morphine antagonist. Wilhelm Feldberg and Derek George Smyth in 1977 confirmed this claim, finding β-endorphin to be much stronger than morphine. They identified that β-endorphin produced strong analgesic effects. In 1976, Choh Hao Li and David Chung recorded the sequences of α-, β-, and γ-endorphin isolated from camel pituitary glands for their opioid activity. This term was essentially assigned to any peptide that demonstrated morphine-like activity. Simon, who independently discovered opioid receptors, would later term these peptides as endorphins. Snyder isolated morphine-like peptides from calf brain. Research during this time was focused on the search for a painkiller that did not have the addictive character or overdose risk of morphine.
![β-endorphin β-endorphin](https://c8.alamy.com/comp/2BC9GEC/beta-endorphin-chemical-formula-science-symbol-elements-reaction-2BC9GEC.jpg)
This came after the discovery of a receptor that was proposed to produce the pain-relieving analgesic effects of morphine and other opioids, which led Kosterlitz and Hughes to their discovery of the endogenous opioid ligands.
![β-endorphin β-endorphin](https://previews.123rf.com/images/molekuul/molekuul1708/molekuul170800036/84063384-beta-endorphin-endogenous-opioid-peptide-molecule-skeletal-formula-.jpg)
They isolated " enkephalins" (from the Greek εγκέφαλος, cerebrum) from pig brain, identified as Met-enkephalin and Leu-enkephalin. In trazodone treated rats, brain β-endorphins were significantly higher on day 28 (929 ± 18.13 pg/g) compared with the levels measured on day 1 and day 9 of treatment (P = 0.001 both), showing slightly higher values than in control rats, yet without statistical significance (P = 0.137).Opioid peptides in the brain were first discovered in 1973 by investigators at the University of Aberdeen, John Hughes and Hans Kosterlitz. Statistical significance was also recorded by comparison of the lower data obtained on day 9 of treatment (433.65 ± 14.67 pg/g) and those observed in the control group (P = 0.001). Data on brain β-endorphin concentration showed a significant decrease on day 1 of trazodone administration (431.03 ± 11.57 pg/g) compared to data obtained from control rat brains (873.5 ± 18.32 pg/g P = 0.001). Endorphin concentrations recorded on day 28 (38.62 ± 1.42 pg/mL) were higher compared to those measured on day 9 (P = 0.439). However, trazodone produced significantly lower β-endorphin concentrations on day 9 of treatment (33.4 ± 1.91 pg/mL) compared to the values measured on day 1 of trazodone administration (P = 0.001). Results: Serum β-endorphins measured on day 1 of trazodone application were significantly higher (72.31 ± 1.86 pg/mL x ± SEM) compared to baseline values (45.83 ± 3.77 pg/mL P = 0.001).