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.
The Columbia Electronic Encyclopedia™ Copyright © 2013, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/

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

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

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

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

peptide

[′pep‚tīd]
(biochemistry)
A compound of two or more amino acids joined by peptide bonds.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

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
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
References in periodicals archive ?
Santiago et al., "Immunoregulatory properties of vasoactive intestinal peptide in human T cell subsets: implications for rheumatoid arthritis," Brain, Behavior, and Immunity, vol.
Delgado, "Vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide inhibit the MEKK1/MEK4/ JNK signaling pathway in endotoxin-activated microglia," Biochemical and Biophysical Research Communications, vol.
Chader, "Interaction of neuropeptides and cultured glial (Muller) cells of the chick retina: elevation of intracellular cyclic AMP by vasoactive intestinal peptide and glucagon," Journal of Neurochemistry, vol.
Hou, "Effect of vasoactive intestinal peptide on gastric adenocarcinoma," Journal of Gastroenterology and Hepatology, vol.
Vasoactive intestinal peptide (VIP) is a 28-amino acid neuropeptide with a broad range of biologic activities.
(4) The vasodilatation is mediated by the release of principally nitric oxide in older individuals whereas other substances such as prostcylcin (6,7) and vasoactive intestinal peptide (VIP) (8) help mediate the response in younger individuals.
Recently, Kimata (2004) recorded increased plasma levels of substance P, vasoactive intestinal peptide, and NGF in patients with self-reported MCS, which support this theory.
Vagal nerve stimulation releases vasoactive intestinal peptide which significantly increases coronary artery blood flow.
Those synthetic peptides mimic the fetal neuroprotective and growth-promoting properties of novel proteins that are regulated by vasoactive intestinal peptide (VIP).
The furthest along in the trial process are granulocyte-macrophage colony-stimulating factor and iontophoretic administration of calcitonin gene-related peptide in combination with vasoactive intestinal peptide.
Pancreatic tumors that secrete too much glucagon or somatostatin can cause diabetes, and too much vasoactive intestinal peptide can cause watery diarrhea.

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