Opioid peptide

 ( Protein Families ) 

Opioid peptides or opiate peptides are that bind to in the brain; and mimic the effect of these peptides. Such peptides may be produced by the body itself, for example endorphins. The effects of these peptides vary, but they all resemble those of opiates. Brain opioid peptide systems are known to play an important role in motivation, emotion, attachment behaviour, the response to stress and pain, control of food intake, and the rewarding effects of alcohol and nicotine.

Opioid-like peptides may also be absorbed from partially digestion food (, Gluten exorphin, and ). Opioid peptides from food typically have lengths between 4–8 . Endogenous opioids are generally much longer.

Opioid peptides are released by post-translational proteolytic cleavage of precursor proteins. The precursors consist of the following components: a Signal peptide that precedes a conserved region of about 50 residues; a variable-length region; and the sequence of the neuropeptides themselves. Sequence analysis reveals that the conserved N-terminal region of the precursors contains 6 , which are probably involved in disulfide bond formation. It is speculated that this region might be important for neuropeptide processing.

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Endogenous The human genome contains several homologous that are known to Genetic code for endogenous opioid peptides.

• The nucleotide sequence of the human gene for proopiomelanocortin (POMC) was characterized in 1980. The POMC gene codes for endogenous opioids such as Beta-endorphin and γ-endorphin.
• The human gene for the was isolated and its sequence described in 1982.
• The human gene for (originally called the "Enkephalin B" gene because of sequence similarity to the enkephalin gene) was isolated and its sequence described in 1983.
• The PNOC gene encoding prepronociceptin, which is cleaved into nociceptin and potentially two additional neuropeptides.
• Adrenorphin, amidorphin, and leumorphin were discovered in the 1980s.
• The were discovered in the 1990s.
• Opiorphin and spinorphin, enkephalinase inhibitors (i.e., prevent the metabolism of enkephalins).
• , hemoglobin-derived opioid peptides, including hemorphin-4, valorphin, and spinorphin, among others.

While not peptides, codeine and morphine are also produced in the human body.

+ Endogenous opioid peptides and their receptors

in particular Table 1: Endogenous opioid peptides.

, citing:

.

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Exogenous Exogenous opioid substances are called , as opposed to endorphins. Exorphins include opioid food peptides, such as gluten exorphin and opioid food peptides, and are often contained in cereals and animal milk. Exorphins mimic the actions of endorphins by binding to and activating in the brain.

Common exorphins include:

• Casomorphin (from casein found in milk of mammals, including cows and humans)
• Gluten exorphin (from gluten found in wheat, rye, barley), including:
• Gliadorphin
• Soymorphin-5 (from soybean)
• Rubiscolin (from spinach)

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Amphibian

• Deltorphin
• Deltorphin I
• Deltorphin II
• Dermorphin

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Synthetic

• Zyklophin – semisynthetic KOR antagonist derived from dynorphin A

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