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organic compound composed of amino acidsamino acid
, any one of a class of simple organic compounds containing carbon, hydrogen, oxygen, nitrogen, and in certain cases sulfur. These compounds are the building blocks of proteins.
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 linked together chemically by peptide bonds. The peptide bond always involves a single covalent link between the α-carboxyl (oxygen-bearing carbon) of one amino acid and the amino nitrogen of a second amino acid. In the formation of a peptide bond from two amino acids, a molecule of water is eliminated. Small peptides with fewer than about ten constituent amino acids are called oligopeptides, and peptides with more than ten amino acids are termed polypeptides. Compounds with molecular weights of more than 10,000 (50–100 amino acids) are usually termed proteins. Organisms commonly contain appreciable quantities of low-molecular-weight peptides some arising from proteins while others are synthesized directly. Certain of these molecules are unusual in that they incorporate amino acids not found in proteins such as amino acids of the d-configuration. Among the biological peptides are many with physiological or antibacterial activity, such as the peptide hormones oxytocinoxytocin
, hormone released from the posterior lobe of the pituitary gland that facilitates uterine contractions and the milk-ejection reflex. The structure of oxytocin, a cyclic peptide consisting of nine amino acids, was determined in 1953 and in the same year it was
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 and vasopressin; adrenocorticotropic hormoneadrenocorticotropic hormone
, polypeptide hormone secreted by the anterior pituitary gland. Its chief function is to stimulate the cortex of the adrenal gland to secrete adrenocortical steroids, chief among them cortisone.
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 (ACTH), secreted by the pituitary gland; and several cyclic peptides, in which the amino-acid sequence forms a ring structure rather than a straight chain, such as the antibiotics tyrocidin and gramicidingramicidin
, antibiotic obtained from the bacterial species Bacillus brevis, which is found in soil. Gramicidin is particularly effective against gram-positive bacteria (see Gram's stain).
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. Laboratory synthesis of peptides has risen to the level of a well-defined art in recent years. Synthetic peptides, composed of as many as a hundred amino acids in specified sequence, have been prepared in the laboratory with good purity and high yields.


A compound that is made up of two or more amino acids joined by covalent bonds which are formed by the elimination of a molecule of H2O from the amino group of one amino acid and the carboxyl group of the next amino acid. Peptides larger than about 50 amino acid residues are usually classified as proteins. Glutathione is the most abundant peptide in mammalian tissue. Hormones such as oxytocin (8), vasopressin (8), glucagon (29), and adrenocorticotropic hormone (39) are peptides whose structures have been deduced; in parentheses are the numbers of amino acid residues for each peptide.

For each step in the biological synthesis of a peptide or protein there is a specific enzyme or enzyme complex that catalyzes each reaction in an ordered fashion along the biosynthetic route. However, it is noteworthy that, although the biological synthesis of proteins is directed by messenger RNA on cellular structures called ribosomes, the biological synthesis of peptides does not require either messenger RNA or ribosomes. See Amino acids, Protein, Ribonucleic acid (RNA), Ribosomes



an organic substance consisting of identical or different amino-acid residues joined by peptide bonds. Peptides are classified according to the number of component amino-acid residues as dipeptides, tripeptides, tetrapeptides, and so on, and as polypeptides.

Small quantities of low-molecular-weight peptides occur in nearly all living cells. For example, the tripeptide glutathione is widely distributed in plant and animal tissues, and the dipeptides anserine and carnosine are present in the muscle tissue of vertebrates. Many natural biologically active substances are classified as peptides, including certain hormones (insulin, adrenocortico-trophic hormone, glucagon, vasopressin, oxytocin), antibiotics (gramicidin, bacillin), and angiotensins and kinins, which are present in blood plasma.

The peptide molecule is a linear or branched chain. If the molecule is linear, it has two termini with one terminal amino group (—NH2) and one terminal carboxyl group (—COOH). Peptides with a closed-chain structure are called cyclopeptides, which include many bacterial toxins, hormones, and antibiotics. Many natural peptides contain amino acids that are not present in proteins, for example, D-amino acids. Peptides exhibit amphoteric properties, give biuret (beginning with tripeptides) and ninhydrin reactions, and dissolve readily in water, acids, and alkalies but are practically insoluble in organic solvents. They decompose upon heating to 200°-300°C.

In living cells, peptides are synthesized from amino acids or formed during the enzymatic breakdown of proteins. Chemical synthesis is used to obtain many biologically active natural peptides and their numerous analogues. Advancements in peptide chemistry have resolved many complex problems in modern biochemistry and molecular biology, such as the deciphering of the genetic code.


Khimiia biologicheski aktivnykh prirodnykh soedinenii. Moscow, 1970.



A compound of two or more amino acids joined by peptide bonds.


any of a group of compounds consisting of two or more amino acids linked by chemical bonding between their respective carboxyl and amino groups
References in periodicals archive ?
Opioid peptides have been localized in a variety of peripheral tissues like placenta, thyroid gland, pancreas, gastrointestinal tract, in the reproductive tract of male and female and in the testis of rats1.
The effect of ethanol on the biosynthesis and regulation of opioid peptides.
morphine) and of endogenous leukocyte-derived opioid peptides (i.
The author also observed an opposite effect in animals treated with naloxone or antiserum to N-acetyl-[beta]-endorphin, suggesting a direct effect of opioid peptides / naloxone in gonads or central nervous system.
In addition to these neural circuits, systems of neurotransmitters and neuromodulators (6) such as GABA, opioid peptides, and endogenously formed cannabinoids (i.
Opioids bind to opiate receptors within the central nervous system (CNS) to activate endogenous opioid peptides, such as endorphins and enkephalins, and produce a change in perception of pain known as analgesia (Vallerand, Sanoski, & Deglin, 2014).
The research on the mechanism of acupuncture analgesia shows that acupuncture may cause nervous system to release opioid peptides with analgesic effect.
In CKD-associated pruritus, it is believed that there exists an imbalance between the endogenous opioid peptides that stimulate and inhibit pruritus pathways (Patel et al.
Steroidal modulation of the regulatory neuropeptides: luteinizing hormone releasing hormone, neuropeptide Y and endogenous opioid peptides.
From the pharmacological point of view, the dose of naloxone used by different research teams is extremely elevated, non physiological: It is known that the use of high doses of Endogenous Opioid Peptides (EOP) antagonists such as naloxone can produce an interaction of the antagonist with other receptors, besides those related to the control of gonadotrophin secretion [21, 31].
The drug candidate NP2 Enkephalin has been engineered to deliver the human Enkephalin gene, which naturally produces opioid peptides involved in pain control, directly to the site of pain in the peripheral nervous system.
In joints, endogenous opioid peptides have been identified in human inflamed synovium, where they are thought to act on intraarticular opioid receptors to reduce joint pain (15).