peptide

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peptide,

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.

Peptide

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

Peptide

 

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.

REFERENCE

Khimiia biologicheski aktivnykh prirodnykh soedinenii. Moscow, 1970.

N. N. CHERNOV

peptide

[′pep‚tīd]
(biochemistry)
A compound of two or more amino acids joined by peptide bonds.

peptide

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 ?
Another important mechanism of degradation of oxidized proteins is their proteolysis in lysosomes containing cathepsins that catalyze the hydrolysis reaction of oxidatively damaged polypeptide chains of proteins.
Student 2 adds the second bead to the string, or the growing polypeptide chain.
These coefficients indicate two important aspects: a) only about 35 % of all polypeptide chains are shared, on average, between trees of any two populations, what does not seem different from what is observed within populations.
The VEGF is a homodimer that comprises 2 polypeptide chains and has a molecular mass of approximately 45 kDa; the single stranded form has a molecular weight of about 23 kDa under denaturing conditions.
Afibrinogenemia occurs as a result of mutation in one of the three genes (FGA, FGB, FGG) which code the three polypeptide chains of fibrinogen on the fourth chromosome (2, 3).
Molecular weght estimation of polypeptide chains by electrophoresis in sodium dodecyl sulphate polyacrylamide gel electrophoresis.Biochem.Biophys.Res.Commun.
The hands of the jelly crystal children are twisted over each other to represent the gelatin polypeptide chains. When the (hot) water and jelly crystal children are mixed, the jelly crystal children are individually surrounded by water particles to simulate dissolving of the crystals.
Vitamin C plays a critical role in the formation of procollagen's polypeptide chains as well as its final conversion into collagen.
Thalassemias are characterized by reduced or absent production of one or more globin chains in the Hb A structure, which is a tetramer consisting of two pairs of globin polypeptide chains: one pair of alpha chains and one pair of beta chains [1].
Proteins are long polypeptide chains ranging from one hundred to several thousand amino acid residues and can adapt to different geometries.
The collagen superfamily today includes at least 27 collagen types with at least 42 distinct polypeptide chains, and > 20 additional proteins with collagen-like domains (Myllyharju and Kivirikko 2004).
Importantly, this gene expression technology can potentially provide the same advantages to the production of therapeutic protein products, including those comprised of multiple subunits or polypeptide chains, such as Factor VIII, a blood clotting factor, as well as chimeric proteins such as TNF-alpha IgG (infliximab).