Opioid peptide
Encyclopedia
Opioid peptides are short sequences of amino acid
s that bind to opioid receptor
s in the brain; opiate
s and opioid
s mimic the effect of these peptides. Opioid peptides may be produced by the body itself, for example endorphin
s. The effects of these peptides vary, but they all resemble opiates. Brain opioid peptide systems are known to play an important role in motivation
, emotion
, attachment behaviour
, the response to stress
and pain
, and the control of food intake
.
Opioid-like peptides may also be absorbed from partially digested
food
(casomorphin
s, exorphins, and rubiscolin
s), but have limited physiological activity. The opioid food peptides
have lengths of typically 4-8 amino acids. The body's own opioids are generally much longer.
contains three homologous
gene
s that are known to code
for endogenous opioid peptides. Each gene codes for a large protein
that can be processed
to yield smaller peptide
s that have opiate
-like activity.
Opioid food
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
s that bind to opioid receptor
Opioid receptor
Opioid receptors are a group of G protein-coupled receptors with opioids as ligands. The endogenous opioids are dynorphins, enkephalins, endorphins, endomorphins and nociceptin. The opioid receptors are ~40% identical to somatostatin receptors...
s in the brain; opiate
Opiate
In medicine, the term opiate describes any of the narcotic opioid alkaloids found as natural products in the opium poppy plant.-Overview:Opiates are so named because they are constituents or derivatives of constituents found in opium, which is processed from the latex sap of the opium poppy,...
s and opioid
Opioid
An opioid is a psychoactive chemical that works by binding to opioid receptors, which are found principally in the central and peripheral nervous system and the gastrointestinal tract...
s mimic the effect of these peptides. Opioid peptides may be produced by the body itself, for example endorphin
Endorphin
Endorphins are endogenous opioid peptides that function as neurotransmitters. They are produced by the pituitary gland and the hypothalamus in vertebrates during exercise, excitement, pain, consumption of spicy food, love and orgasm, and they resemble the opiates in their abilities to produce...
s. The effects of these peptides vary, but they all resemble opiates. Brain opioid peptide systems are known to play an important role in motivation
Motivation
Motivation is the driving force by which humans achieve their goals. Motivation is said to be intrinsic or extrinsic. The term is generally used for humans but it can also be used to describe the causes for animal behavior as well. This article refers to human motivation...
, emotion
Emotion
Emotion is a complex psychophysiological experience of an individual's state of mind as interacting with biochemical and environmental influences. In humans, emotion fundamentally involves "physiological arousal, expressive behaviors, and conscious experience." Emotion is associated with mood,...
, attachment behaviour
Attachment theory
Attachment theory describes the dynamics of long-term relationships between humans. Its most important tenet is that an infant needs to develop a relationship with at least one primary caregiver for social and emotional development to occur normally. Attachment theory is an interdisciplinary study...
, the response to stress
Stress (biology)
Stress is a term in psychology and biology, borrowed from physics and engineering and first used in the biological context in the 1930s, which has in more recent decades become commonly used in popular parlance...
and pain
Pain
Pain is an unpleasant sensation often caused by intense or damaging stimuli such as stubbing a toe, burning a finger, putting iodine on a cut, and bumping the "funny bone."...
, and the control of food intake
Hunger (motivational state)
Hunger is a sensation experienced when one is required to eat food. In contrast Satiety is the absence of hunger; it is the sensation of feeling full. Appetite is another sensation experienced with eating, however, it differs from hunger; it is the desire to eat food without a physiological need...
.
Opioid-like peptides may also be absorbed from partially digested
Digestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....
food
Food
Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals...
(casomorphin
Casomorphin
Casomorphins are peptides, i.e., protein fragments, derived from the digestion of milk protein casein. The distinguishing characteristic of casomorphins is that they have an opioid effect....
s, exorphins, and rubiscolin
Rubiscolin
The rubiscolins are a group of opioid peptides which are formed during digestion of the ribulose bisphosphate carboxylase/oxygenase protein from spinach leaves. Rubiscolins mimic the effects of opiates and therefore influence the brain...
s), but have limited physiological activity. The opioid food peptides
Opioid food peptides
Opioid food peptides include:*Casomorphin *Gluten exorphin *Gliadorphin/gluteomorphin *Rubiscolin...
have lengths of typically 4-8 amino acids. The body's own opioids are generally much longer.
Opioid peptides produced by the body
The human genomeGenome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
contains three homologous
Homology (biology)
Homology forms the basis of organization for comparative biology. In 1843, Richard Owen defined homology as "the same organ in different animals under every variety of form and function". Organs as different as a bat's wing, a seal's flipper, a cat's paw and a human hand have a common underlying...
gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
s that are known to code
Genetic code
The genetic code is the set of rules by which information encoded in genetic material is translated into proteins by living cells....
for endogenous opioid peptides. Each gene codes for a large protein
Protein precursor
A protein precursor, also called a pro-protein or pro-peptide, is an inactive protein that can be turned into an active form by posttranslational modification. The name of the precursor for a protein is often prefixed by pro...
that can be processed
Protease
A protease is any enzyme that conducts proteolysis, that is, begins protein catabolism by hydrolysis of the peptide bonds that link amino acids together in the polypeptide chain forming the protein....
to yield smaller peptide
Peptide
Peptides are short polymers of amino acid monomers linked by peptide bonds. They are distinguished from proteins on the basis of size, typically containing less than 50 monomer units. The shortest peptides are dipeptides, consisting of two amino acids joined by a single peptide bond...
s that have opiate
Opiate
In medicine, the term opiate describes any of the narcotic opioid alkaloids found as natural products in the opium poppy plant.-Overview:Opiates are so named because they are constituents or derivatives of constituents found in opium, which is processed from the latex sap of the opium poppy,...
-like activity.
- The nucleotide sequence of the human gene for proopiomelanocortinProopiomelanocortinPro-opiomelanocortin is a precursor polypeptide with 241 amino acid residues. POMC is synthesized from the 285-amino acid long polypeptide precursor, pre-pro-opiomelanocortin , by the removal of a 44-amino acid long signal peptide sequence during translation.The POMC gene is located on chromosome...
(POMC) was characterized in 1980. The POMC gene codes for endogenous opiates such as β-endorphinBeta-endorphinβ-endorphin is an endogenous opioid peptide neurotransmitter found in the neurons of both the central and peripheral nervous system.The amino acid sequence is:...
and gamma-endorphin. The peptides with opiate activityOpioid receptorOpioid receptors are a group of G protein-coupled receptors with opioids as ligands. The endogenous opioids are dynorphins, enkephalins, endorphins, endomorphins and nociceptin. The opioid receptors are ~40% identical to somatostatin receptors...
that are derived from proopiomelanocortin comprise the class of endogenous opioid peptides called "endorphins". - The human gene for enkephalinEnkephalinAn enkephalin is a pentapeptide involved in regulating nociception in the body. The enkephalins are termed endogenous ligands, or specifically endorphins, as they are internally derived and bind to the body's opioid receptors. Discovered in 1975, two forms of enkephalin were revealed, one...
s was isolated and its sequence described in 1982. - The human gene for dynorphinDynorphinDynorphins are a class of opioid peptides that arise from the precursor protein prodynorphin. When prodynorphin is cleaved during processing by proprotein convertase 2 , multiple active peptides are released: dynorphin A, dynorphin B, and α/β-neo-endorphin...
s (originally called the "Enkephalin B" gene because of sequence similarity to the enkephalin gene) was isolated and its sequence described in 1983. - AdrenorphinAdrenorphinAdrenorphin, also sometimes referred to as metorphamide, is an endogenous, C-terminally amidated, opioid octapeptide that is produced from proteolyic cleavage of proenkephalin A and is widely distributed throughout the mammalian brain...
and amidorphinAmidorphinAmidorphin is an endogenous, C-terminally amidated, opioid peptide generated as a cleavage product of proenkephalin A that is widely distributed in the mammalian brain, with particularly high concentrations found in the adrenal medulla, posterior pituitary, and striatum...
were discovered in the 1980s. - OpiorphinOpiorphinOpiorphin is an endogenous chemical compound first isolated from human saliva. Initial research with mice shows the compound has a painkilling effect greater than that of morphine. It works by stopping the normal breakdown of enkephalins, natural pain-killing opioids in the spinal cord...
, found in human saliva, is an enkephalinase inhibitor, i.e. it prevents the metabolism of enkephalins.
Opioid foodFoodFood is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals...
peptides
- CasomorphinCasomorphinCasomorphins are peptides, i.e., protein fragments, derived from the digestion of milk protein casein. The distinguishing characteristic of casomorphins is that they have an opioid effect....
(from milkMilkMilk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many...
) - Gluten exorphin (from glutenGlutenGluten is a protein composite found in foods processed from wheat and related grain species, including barley and rye...
) - Gliadorphin/gluteomorphinGliadorphinGliadorphin is an opioid peptide that is formed during digestion of the gliadin component of the gluten protein. It is usually broken down into amino acids by digestion enzymes. It has been hypothesized that children with autism have abnormal leakage from the gut of this compound, which then...
(from glutenGlutenGluten is a protein composite found in foods processed from wheat and related grain species, including barley and rye...
) - RubiscolinRubiscolinThe rubiscolins are a group of opioid peptides which are formed during digestion of the ribulose bisphosphate carboxylase/oxygenase protein from spinach leaves. Rubiscolins mimic the effects of opiates and therefore influence the brain...
(from spinachSpinachSpinach is an edible flowering plant in the family of Amaranthaceae. It is native to central and southwestern Asia. It is an annual plant , which grows to a height of up to 30 cm. Spinach may survive over winter in temperate regions...
)
Microbial opioid peptides
- Deltorphin I and II (fungalFungusA fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...
) - Dermorphin (from an unknown microbe)