Difference between revisions of "Peptide" - New World Encyclopedia

Latest revision as of 20:16, 14 April 2015

Peptides are short chains of amino acids linked together via peptide bonds and having a defined sequence. Peptides function primarily as signaling molecules in animals or as antibiotics in some lower organisms.

The number of amino acid molecules present in a peptide is indicated by a prefix. For example, a dipeptide has two amino acids; a tripeptide has three. An oligopeptide contains a few molecules; a polypeptide contains many. Peptides generally contain fewer than 30 amino acid residues, while polypeptides contain as many as 4000. The distinction between polypeptides and proteins is largely academic and imprecise, and the two terms are sometimes used interchangeably. However, there is a movement within the scientific community to define proteins as polypeptides (or complexes of polypeptides) with three-dimensional structure.

In animals, peptides are involved in the complex coordination of the body, with three major classes of peptides involved in signaling:

Peptide hormones, which function as chemical messengers between cells. Growth hormone, for example, is involved in the general stimulation of growth, and insulin and glucagon are well known peptide hormones.
Neuropeptides, which are peptides found in neural tissue. Endorphins and enkephalins are neuropeptides that mimic the effects of morphine, inhibiting the transmission of pain signals. The peptides vasopressin and oxytoxin have been linked to social behaviors such as pair-bonding.
Growth factors, which play a role in regulating animal cell growth and differentiation.

Human creativity has led to peptides being important tools for understanding protein structure and function. Peptide fragments are components of proteins that researchers use to identify or quantify the source protein. Often these fragments are the products of enzymatic degradation performed in the laboratory on a controlled sample, but they can also be forensic or paleontological samples that have been degraded by natural effects. Peptides also allow antibodies to be generated without the need to purify the protein of interest, by making antigenic peptides of sections of the protein.

The components of peptides

Summary of the formation of a peptide bond. Click on image to see the reaction.

Like proteins, peptides are built from combinations of 20 different amino acids, which are organic molecules composed of an amino group (-NH2), a carboxylic acid group (-COOH), and a unique R group, or side chain. Two amino acids (specifically, alpha-amino acids) are linked together by a peptide bond. A peptide bond is a chemical bond formed between two molecules when the carboxyl group of one amino acid reacts with the amino group of the other amino acid; the resulting CO-NH bond is called a peptide bond. An amino acid residue is what is left of an amino acid once it has coupled with another amino acid to form a peptide bond.

Peptides are then created by the polymerization of amino acids, a process in which amino acids are joined together in chains. Shorter strings of amino acids may be referred to as peptides, or, less commonly, oligopeptides.

Peptide synthesis

Peptides are synthesized from amino acids according to an mRNA template, which is itself synthesized from a DNA template inside the cell's nucleus. The precursors of ribosomal peptides are processed in several stages in the endoplasmic reticulum, resulting in "propeptides." These propeptides are then packaged into membrane-bound secretory vesicles, which can be released into the bloodstream in response to specific stimuli.

Nonribosomal peptides, found primarily in fungi, plants, and, unicellular organisms are synthesized using a modular enzyme complex (which functions much like a conveyor belt in a factory). All of these complexes are laid out in a similar fashion, and they may contain many different modules to perform a diverse set of chemical manipulations on the developing peptide. Nonribosomal peptides often have highly complex cyclic structures, although linear nonribosomal peptides are also common.

Some key peptide groups and their biological function

Peptides comprise the widest variety of signaling molecules in animals. The three major classes of peptides are peptide hormones, neuropeptides, and polypeptide growth factors. Many peptides are found in both the brain and non neural tissues. The blood-brain barrier prevents peptide hormones traveling in the blood from entering the brain, so that they do not interfere with the functioning of the central nervous system.

Peptide hormones

Peptide hormones are a class of peptides that function in living animals as chemical messengers from one cell (or group of cells) to another. Well-known peptide hormones include insulin, glucagon, and the hormones secreted from the pituitary gland, an endocrine gland about the size of a pea that sits in a small, bony cavity at the base of the brain. The latter include follicle stimulating hormone (FSH), growth hormone, and vasopressin. However, peptide hormones are produced by many different organs and tissues, including the heart, pancreas, and gastrointestinal tract.

Neuropeptides

A neuropeptide is any of the variety of peptides found in neural tissue. Approximately 100 different peptides are currently known to be released by different populations of neurons in the mammalian brain. Some neuropeptides act both as neurotransmitters in the nervous system and as neurohormones that act on distant cells.

Neurons use many different chemical signals to communicate information, including neurotransmitters, peptides, cannabinoids, and even some gases, like nitric oxide. Peptide signals play a role in information processing distinct from that of conventional neurotransmitters. While neurotransmitters generally affect the excitability of other neurons by depolarizing them or hyperpolarizing them, peptides have much more diverse effects; among other things, they can affect gene expression, local blood flow, and the formation of synapses.

Neurons very often produce both a conventional neurotransmitter (such as glutamate, GABA or dopamine) and one or more neuropeptides. Peptides are generally packaged in large dense-core vesicles, while the co-existing neurotransmitters are contained in small synaptic vesicles.

Vasopressin and oxytoxin

The neuropeptide Arginine vasopressin (AVP), also known as argipressin or antidiuretic hormone (ADH), is a hormone found in humans. It is mainly released when the body is low on water; it stimulates water reabsorption in the kidneys. It performs diverse actions when released in the brain, and has been implicated in memory formation, aggression, blood pressure regulation, and temperature regulation. Similar vassopressins are found in other mammalian species.

In recent years, there has been particular interest in the role of vasopressin in social behavior. It is thought that vasopressin, released into the brain during sexual activity, initiates and sustains patterns of activity that support the pair-bond between the sexual partners; in particular, vasopressin seems to induce the male to become aggressive towards other males. Evidence for this connection comes from experimental studies on several species which indicate that the precise distribution of vasopressin and vasopressin receptors in the brain is associated with species-typical patterns of social behavior. In particular, there are consistent differences between monogamous species and promiscuous species in the distribution of vasopressin receptors, and sometimes in the distribution of vasopressin-containing axons, even when closely-related species are compared. Moreover, studies involving either injecting vasopressin agonists into the brain or blocking the actions of vasopressin support the hypothesis that vasopressin is involved in aggression towards other males. There is also evidence that differences in the vasopressin receptor gene between individual members of a species might be predictive of differences in social behavior.

Oxytocin is a mammalian hormone involved in the stimulation of smooth muscle contraction that also acts as a neurotransmitter in the brain. In women, it is released mainly after distension of the cervix and vagina during labor, and after stimulation of the nipples, facilitating birth and breastfeeding, respectively.

Opioid peptides

Opioid peptides produced in the body include endorphins and enkephalins. Opioid peptides act as natural pain killers, or opiates, decreasing pain responses in the central nervous system.

Growth factors

Polypeptide growth factors control animal cell growth and differentiation. Nerve growth factor (or NGF) is involved in the development and survival of neurons, while platelet-derived growth factor (PDGF) participates in blood clotting at the site of a wound. PDGF stimulates the spread of fibroblasts in the vicinity of the clot, facilitating the regrowth of the damaged tissue.

Given the role of polypeptide growth factors in controlling cell proliferation, abnormalities in growth factor signaling are the basis for a variety of diseases, including many types of cancer.

Peptides are an important research tool

Peptides have received prominence in molecular biology in recent times for several reasons:

Peptides allow researchers to generate antibodies in animals without the need to purify the protein of interest. The researcher can simply make antigenic peptides of sections of the protein.
Peptides have become instrumental in mass spectrometry, allowing the identification of proteins of interest based on peptide masses and sequences.
Peptides have recently been used in the study of protein structure and function. For example, synthetic peptides can be used as probes to determine where protein-peptide interactions occur.
Inhibitory peptides are also used in clinical research to examine the effects of peptides on the inhibition of cancer proteins and other diseases.

Peptide families

Below is a more detailed list of the major families of ribosomal peptides:

Vasopressin and oxytocin
- Vasopressin
- Oxytocin

The Tachykinin peptides
- Substance P
- Kassinin
- Neurokinin A
- Eledoisin
- Neurokinin B

Vasoactive intestinal peptides
- VIP (Vasoactive intestinal peptide)
- PACAP (Pituitary adenylate cyclase activating peptide)
- PHI 27
- PHM 27
- GHRH 1-24 (Growth hormone releasing hormone 1-24)
- Glucagon
- Secretin

Pancreatic polypeptide-related peptides
- NPY
- PYY (Peptide YY)
- APP (Avian pancreatic polypeptide)
- HPP (Human pancreatic polypeptide)

Opioid peptides
- Proopiomelanocortin (POMC) Peptides
- The Enkephalin pentapeptides
- The Prodynorphin peptides

Calcitonin peptides
- Calcitonin
- Amylin
- AGG01

References
ISBN links support NWE through referral fees

Cooper, G. M., and R. E. Hausman. 2004. The Cell: A Molecular Approach, 3rd edition. Washington, DC: ASM Press & Sunderland, MA: Sinauer Associates. ISBN 0878932143
Lodish, H., D. Baltimore, A. Berk, S. L. Zipursky, P. Matsudaira, and J. Darnell. 1996. Molecular Cell Biology. Oxford: W H Freeman and Company. ISBN 0716727110
Stryer, L. 1995. Biochemistry, 4th edition. New York, NY: W.H. Freeman. ISBN 0716720094

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@@ Line 1: / Line 1: @@
-{{Claimed}}{{Contracted}}
+{{Paid}}{{Approved}}{{Images OK}}{{Submitted}}{{copyedited}}
-'''Peptides''' (from the Greek πεπτος, "digestible") are a family of [[organic compound]]s that consist of short chains of [[amino acid]]s linked together via [[peptide bond]]s. They function primarily as [[hormone]]s, signaling molecules, or [[antibiotic]]s in living organisms.
+'''Peptides''' are short chains of [[amino acid]]s linked together via [[#The components of peptides|peptide bond]]s and having a defined sequence. Peptides function primarily as '''[[signaling molecules]]''' in [[animal]]s or as [[antibiotic]]s in some lower [[organism]]s.
-The number of amino-acid molecules present in a peptide is indicated by a prefix. For example, a ''dipeptide'' has two amino acids; a ''tripeptide'', three. An ''oligopeptide'' contains a few molecules; a ''polypeptide'', many. The distinction between polypeptides and [[protein]]s is largely academic and imprecise. One convention places an informal dividing line at approximately 50 amino acids in length. However, this definition is somewhat arbitrary — some peptides such as [[amyloid beta|alzheimer's beta peptide]] can be considered proteins, and some proteins (such as [[insulin]]) are close to the upper limit for peptides. There is a considerable movement within the scientific community to ascribe the more specific definition that "a peptide is an amino acid molecule without secondary structure; on gaining defined structure, it is a protein." Thus, the same molecule could be classified as either a peptide or a protein depending on its environment (though there are peptides that cannot be proteins).
+The number of amino acid molecules present in a peptide is indicated by a prefix. For example, a ''dipeptide'' has two amino acids; a ''tripeptide'' has three. An ''oligopeptide'' contains a few molecules; a ''polypeptide'' contains many. Peptides generally contain fewer than 30 amino acid residues, while polypeptides contain as many as 4000. The distinction between polypeptides and [[protein]]s is largely academic and imprecise, and the two terms are sometimes used interchangeably. However, there is a movement within the scientific community to define proteins as polypeptides (or complexes of polypeptides) with three-dimensional structure.
-Functions of peptides in body and in research
+In animals, peptides are involved in the complex coordination of the body, with three major classes of peptides involved in signaling:
+*'''[[Peptide hormones]]''', which function as chemical messengers between [[cell (biology)|cells]]. [[Growth hormone]], for example, is involved in the general stimulation of growth, and [[insulin]] and [[glucagon]] are well known peptide hormones.
+*'''[[Neuropeptides]]''', which are peptides found in [[neural tissue]]. [[Endorphin]]s and [[enkephalin]]s are neuropeptides that mimic the effects of [[morphine]], inhibiting the transmission of [[pain]] signals. The peptides [[vasopressin]] and [[oxytoxin]] have been linked to social behaviors such as pair-bonding.
+*'''[[Growth factors]]''', which play a role in regulating animal cell growth and differentiation.
+{{toc}}
+Human creativity has led to peptides being important tools for understanding protein structure and function. '''Peptide fragments''' are components of proteins that researchers use to identify or quantify the [[source protein]]. Often these fragments are the products of enzymatic degradation performed in the laboratory on a controlled sample, but they can also be forensic or paleontological samples that have been degraded by natural effects. Peptides also allow [[antibody|antibodies]] to be generated without the need to purify the protein of interest, by making [[antigen|antigenic]] peptides of sections of the protein.
-==The components of peptides==
+== The components of peptides ==
 [[Image:Peptide_bonding.gif|thumb|Summary of the formation of a peptide bond. Click on image to see the reaction.]]
-Like proteins, peptides are built from combinations of 20 different '''amino acids''', which are organic molecules composed of an amino group (-NH2), a carboxylic acid group (-COOH), and a unique R group, or [[side chain]]. Two amino acids (specifically, ''alpha-amino acids'') are linked together by a peptide bond, which forms when the amino group of one amino acid reacts with the carboxyl group of a second amino acid. An amino acid residue is what is left of an amino acid once it has coupled with another amino acid to form a peptide bond.
+Like [[protein]]s, peptides are built from combinations of 20 different amino acids, which are organic molecules composed of an amino group (-NH2), a [[carboxylic acid]] group (-COOH), and a unique R group, or side chain. Two [[amino acid]]s (specifically, alpha-amino acids) are linked together by a peptide bond. A [[peptide bond]] is a chemical bond formed between two [[molecule]]s when the carboxyl group of one amino acid reacts with the amino group of the other amino acid; the resulting CO-NH bond is called a peptide bond. An amino acid residue is what is left of an amino acid once it has coupled with another amino acid to form a peptide bond.
-Peptides are then created by the polymerization of amino acids, a process in which amino acids are joined together in chains. Shorter strings of amino acids may be referred to as polypeptides, peptides, or, less commonly, oligopeptides.
+Peptides are then created by the [[polymer]]ization of amino acids, a process in which amino acids are joined together in chains. Shorter strings of amino acids may be referred to as peptides, or, less commonly, oligopeptides.
-Note the use of peptides in building proteins. '''Peptide fragments''' are components of proteins that research use to identify or quantify the source protein.  Often these fragments are the products of enzymatic degradation performed in the laboratory on a controlled sample, but they can also be forensic or paleontological samples that have been degraded by natural effects.
 ==Peptide synthesis==
-Like protein molecules, '''ribosomal peptides''' are synthesized from amino acids according to an [[mRNA]] template, which is itself synthesized from a [[DNA]] template inside the [[cell (biology)|cell]]'s [[Cell nucleus|nucleus]]. Peptide precursors are then processed in several stages, typically in the [[endoplasmic reticulum]], resulting in "propeptides". The propeptides are then packaged into membrane-bound secretory vesicles, which can be released into the bloodstream in response to specific stimuli.
+Peptides are synthesized from amino acids according to an [[mRNA]] template, which is itself synthesized from a [[DNA]] template inside the [[cell (biology)|cell]]'s nucleus. The precursors of '''ribosomal peptides''' are processed in several stages in the [[endoplasmic reticulum]], resulting in "propeptides." These propeptides are then packaged into membrane-bound secretory [[vesicle]]s, which can be released into the bloodstream in response to specific stimuli.
-'''Nonribosomal peptides''', found primarily in [[unicellular organism]]s, [[plant]]s, and [[fungi]], are synthesized using a [[Modularity (biology)|modular]] enzyme complex (which functions much like a conveyor belt in a factory). All of these complexes are laid out in a similar fashion, and they can contain many different modules to perform a diverse set of chemical manipulations on the developing peptide. In general, nonribosomal peptides often have highly complex cyclic structures, although linear nonribosomal peptides are also common.
+'''Nonribosomal peptides,''' found primarily in [[fungi]], [[plant]]s, and, unicellular organisms are synthesized using a modular enzyme complex (which functions much like a conveyor belt in a factory). All of these complexes are laid out in a similar fashion, and they may contain many different modules to perform a diverse set of chemical manipulations on the developing peptide. Nonribosomal peptides often have highly complex cyclic structures, although linear nonribosomal peptides are also common.
 ==Some key peptide groups and their biological function==
-Ribosomal peptides function as [[hormone]]s and signaling molecules, typically in higher organisms. Some lower organisms produce peptides as antibiotics, such as [[microcin J25]].
+Peptides comprise the widest variety of [[signaling molecules]] in animals. The three major classes of peptides are ''peptide hormones,'' ''neuropeptides,'' and ''polypeptide growth factors.'' Many peptides are found in both the brain and non neural tissues. The [[blood-brain barrier]] prevents peptide hormones traveling in the [[blood]] from entering the [[brain]], so that they do not interfere with the functioning of the [[central nervous system]].
 === Peptide hormones ===
-'''Peptide hormones''' are a class of peptides that function in living animals as ‘’hormones’’ - i.e., as chemical messengers from one cell (or group of cells) to another.
+'''Peptide hormones''' are a class of peptides that function in living [[animal]]s as chemical messengers from one cell (or group of cells) to another. Well-known peptide hormones include [[insulin]], [[glucagon]], and the hormones secreted from the [[pituitary gland]], an [[endocrine gland]] about the size of a pea that sits in a small, bony cavity at the base of the [[brain]]. The latter include [[follicle stimulating hormone]] (FSH), [[growth hormone]], and [[vasopressin]]. However, peptide hormones are produced by many different [[organ]]s and [[tissue]]s, including the [[heart]], [[pancreas]], and [[gastrointestinal tract]].
-Several important peptide hormones are secreted from the [[pituitary gland]], an [[endocrine gland]] about the size of a pea that sits in a small, bony cavity at the base of the [[brain]]. The [[anterior pituitary]] secretes [[luteinizing hormone]] and [[follicle stimulating hormone]], which act on the [[gonads]]; [[prolactin]], which acts on the [[mammary gland]], [[adrenocorticotrophic hormone]] (ACTH), which acts on the [[adrenal cortex]] to regulate the secretion of [[glucocorticoids]]; and [[growth hormone]], which acts on [[bone]], [[muscle]] and the [[liver]]. The [[posterior pituitary]] gland secretes [[vasopressin]], and [[oxytocin]]. Peptide hormones are produced by many different organs and tissues, however, including the [[heart]] ([[atrial-natriuretic peptide]] (ANP) or atrial natriuretic factor (ANF)) and [[pancreas]] ([[insulin]] and [[somatostatin]]), the gastrointestinal tract ([[cholecystokinin]], [[gastrin]]), and [[fat]] stores ([[leptin]]).
-'''Arginine vasopressin''' ('''AVP'''), also known as '''argipressin''' or '''antidiuretic hormone''' ('''ADH'''), is a human [[hormone]] that is mainly released when the body is low on [[water]]; it causes the [[kidney]]s to conserve water by concentrating the [[urine]] and reducing urine volume. It also has various functions in the [[brain]] and [[blood vessel]]s.
-Vasopressin released within the brain has many actions:
-* It has been implicated in [[memory]] formation, including delayed reflexes, image, short- and long-term memory, though the mechanism remains unknown, and these findings are controversial.  However, the synthetic [[vasopressin analogue]] [[desmopressin]] has come to interest as a likely [[nootropic]].
-* Vasopressin is released into the brain in a [[circadian rhythm]] by neurons of the [[Suprachiasmatic nucleus|suprachiasmatic nucleus of the hypothalamus]].
-* Vasopressin released from centrally-projecting hypothalamic neurons is involved in aggression, blood pressure regulation and temperature regulation.
-In recent years there has been particular interest in the role of vasopressin in social behavior. It is thought that vasopressin, released into the brain during sexual activity, initiates and sustains patterns of activity that support the pair-bond between the sexual partners; in particular, vasopressin seems to induce the male to become aggressive towards other males.
-Evidence for this comes from experimental studies, in several species, which indicate that the precise distribution of vasopressin and vasopressin receptors in the brain is associated with species-typical patterns of social behavior. In particular, there are consistent differences between monogamous species and promiscuous species in the distribution of vasopressin receptors, and sometimes in the distribution of vasopressin-containing axons, even when closely-related species are compared. Moreover, studies involving either injecting vasopressin agonists into the brain, or blocking the actions of vasopressin, support the hypothesis that vasopressin is involved in aggression towards other males. There is also evidence that differences in the vasopressin receptor gene between individual members of a species might be predictive of differences in social behavior.
-'''Oxytocin''' (Greek: "quick birth") is a [[mammal]]ian [[hormone]] that also acts as a [[neurotransmitter]] in the [[brain]]. In women, it is released mainly after distension of the [[cervix]] and [[vagina]] during labor, and after stimulation of the [[nipple]]s, facilitating [[childbirth|birth]] and [[breastfeeding]], respectively. Oxytocin is released during [[orgasm]] in both sexes. In the brain, oxytocin is involved in social recognition and bonding, and might be involved in the formation of trust between people.
-Many [[neurotransmitters]] are secreted and released in a similar fashion to peptide hormones, and some '[[neuropeptides]]' may be used as neurotransmitters in the [[nervous system]] in addition to acting as hormones when released into the blood.
 === Neuropeptides ===
-A '''neuropeptide''' is any of the variety of peptides found in [[neural tissue]]; e.g. [[endorphin]]s and [[enkephalin]]s. Approximately 100 different peptides are currently known to be released by different populations of neurons in the mammalian brain.
+A '''neuropeptide''' is any of the variety of peptides found in [[neural tissue]]. Approximately 100 different peptides are currently known to be released by different populations of neurons in the [[mammal]]ian brain. Some neuropeptides act both as [[neurotransmitter]]s in the [[nervous system]] and as neurohormones that act on distant cells.
-Neurons use many different chemical signals to communicate information, including neurotransmitters, peptides, [[cannabinoids]], and even some gases, like [[nitric oxide]]. Peptide signals play a role in information processing that is different to that of conventional neurotransmitters, and many appear to be particularly associated with specific behaviors. For example, [[oxytocin]] and [[vasopressin]] have striking and specific effects on social behaviors, including maternal behavior and pair bonding.
+[[Neuron]]s use many different chemical signals to communicate information, including neurotransmitters, peptides, [[cannabinoids]], and even some gases, like [[nitric oxide]]. Peptide signals play a role in information processing distinct from that of conventional neurotransmitters. While neurotransmitters generally affect the excitability of other neurons by depolarizing them or hyperpolarizing them, peptides have much more diverse effects; among other things, they can affect gene expression, local blood flow, and the formation of [[synapse]]s.
-[[Neurotransmitters]] generally affect the excitability of other neurons, by depolarizing them or by hyperpolarizing them. Peptides have much more diverse effects; among other things, they can affect gene expression, local blood flow, [[synaptogenesis]], and [[glial]] cell morphology. Peptides tend to have prolonged actions, and some have striking effects on behavior.
+Neurons very often produce both a conventional neurotransmitter (such as [[glutamate]], [[GABA]] or [[dopamine]]) and one or more neuropeptides. Peptides are generally packaged in large dense-core vesicles, while the co-existing neurotransmitters are contained in small synaptic vesicles.
-Neurons very often produce both a conventional neurotransmitter (such as [[glutamate]], [[GABA]] or [[dopamine]]) and one or more neuropeptides. Peptides are generally packaged in large dense-core vesicles, while the co-existing neurotransmitters are contained in small synaptic vesicles. The large dense-core vesicles are often found in all parts of a neuron, including the [[soma]], [[dendrites]], axonal swellings and nerve endings, whereas the small synaptic vesicles are mainly found in clusters at presynaptic locations.
+====Vasopressin and oxytoxin====
+The neuropeptide '''Arginine vasopressin''' (AVP), also known as '''argipressin''' or '''antidiuretic hormone''' (ADH), is a [[hormone]] found in [[human]]s. It is mainly released when the body is low on [[water]]; it stimulates water reabsorption in the [[kidney]]s. It performs diverse actions when released in the brain, and has been implicated in [[memory]] formation, aggression, blood pressure regulation, and temperature regulation. Similar vassopressins are found in other mammalian species.
-=== Opioid peptides ===
+In recent years, there has been particular interest in the role of vasopressin in [[social behavior]]. It is thought that vasopressin, released into the brain during sexual activity, initiates and sustains patterns of activity that support the pair-bond between the sexual partners; in particular, vasopressin seems to induce the male to become aggressive towards other males. Evidence for this connection comes from experimental studies on several species which indicate that the precise distribution of vasopressin and vasopressin receptors in the brain is associated with species-typical patterns of social behavior. In particular, there are consistent differences between monogamous species and promiscuous species in the distribution of vasopressin receptors, and sometimes in the distribution of vasopressin-containing [[axons]], even when closely-related species are compared. Moreover, studies involving either injecting vasopressin agonists into the brain or blocking the actions of vasopressin support the hypothesis that vasopressin is involved in aggression towards other males. There is also evidence that differences in the vasopressin receptor gene between individual members of a species might be predictive of differences in social behavior.
-An '''opioid''' is a chemical substance (natural or synthetic) that has a morphine-like action in the body. Its main use is for [[analgesia|pain relief]]. These agents work by binding to [[opioid receptor]]s, which are found principally in the [[central nervous system]] and the [[gastrointestinal tract]]. Opioid peptides that are produced in the body include [[endorphin]]s, [dynorphin]]s, and [[enkephalin]]s.
-When certain food proteins such as [[gluten]], [[casein]], [[egg (food)|egg]] protein, and [[spinach]] protein are broken down, [[opioid peptides]] are formed. These peptides mimic the effects of morphine, and those individuals that are unable to break them down will experience mental illness (vague). A '''gluten-free casein-free diet''' (or '''GFCF diet''') is a restrictive diet which entirely eliminates intake of the naturally-occuring proteins [[gluten]] (found naturally in wheat, barley, and rye), and [[casein]] (found in [[milk]]).  The GFCF diet is recommended by advocacy groups, such as the [[Autism Research Institute]], to reduce the prevalence of certain behaviors associated with pervasive developmental disorders, especially [[autism]].  While multiple success stories have been published and circulated, results from clinical trials and double-blind studies have produced little to confirm the diet's efficacy.
+'''Oxytocin''' is a [[mammal]]ian hormone involved in the stimulation of smooth muscle contraction that also acts as a neurotransmitter in the [[brain]]. In women, it is released mainly after distension of the [[cervix]] and [[vagina]] during [[labor]], and after stimulation of the nipples, facilitating [[childbirth|birth]] and [[breastfeeding]], respectively.
-In the 1960s, Dohan speculated that the low incidence of [[schizophrenia]] in certain South Pacific Island societies was a result of a diet low in wheat- and milk- based foods.<ref> Dohan, F.C. (1966) Cereals and Schizophrenia, data and hypothesis ''Acta Physiologica Scandinavica'', ''42'', 125-132.</ref>  Dohan proposed genetic defect as a probable [[etiology]] for schizophrenia, wherein individuals were incapable of completely metabolizing gluten and casein.  The consequence of incomplete metabolism is excess [[peptide]] levels in the gastrointestinal tract, which Dothan hypothesizes are responsible for schizophrenic behaviors.
+==== Opioid peptides ====
+''Opioid peptides'' produced in the body include [[endorphin]]s and [[enkephalin]]s. Opioid peptides act as natural pain killers, or [[opiate]]s, decreasing [[pain]] responses in the central nervous system.
-The possible relationship between gluten, casein, and autism was first articulated by Kalle Reichelt, M.D. in 1991.<ref> Reichelt KL, Knivsberg A-M, Lind G, Nødland M. Probable etiology and possible treatment of childhood autism. Brain Dysfunct 1991; 4: 308-19 </ref>  Based on studies showing correlation between autism and increased urinary peptide levels, Reichelt hypothesized that some of these peptides may have an [[opiate]] effect.  Further work determined [[opioid peptide]]s such as [[casomorphine]]s<ref> Sun, Z. and Cade, J.R. (1999) A peptide found in schizophrenia and autism causes behavioral changes in rats.  ''Autism'', ''3''(1), 85-95. </ref> (from [[casein]]) and [[gluten exorphine]]s and [[gliadorphin]] (from [[gluten]]) as probable suspects, due to their chemical similarity to opiates.
+=== Growth factors ===
-Reichelt hypothesizes that long term exposure to these [[opiate]] [[peptides]] may have effects on brain maturation and contribute to social awkwardness and isolation.  On this basis, Reichelt and others have proposed a gluten-free casein-free diet to minimize the buildup of opiate peptides and promote typical development of brain function.
+Polypeptide '''growth factors''' control animal cell growth and differentiation. Nerve growth factor (or NGF) is involved in the development and survival of neurons, while platelet-derived growth factor (PDGF) participates in [[blood]] clotting at the site of a wound. PDGF stimulates the spread of [[fibroblast]]s in the vicinity of the clot, facilitating the regrowth of the damaged tissue.
-Reichelt's hypothesis is not generally regarded as a definitive [[etiology]] for autism, nor is the GFCF diet advocated as a "cure".  While considerable attention has been given to metabolic and/or gastrointestinal factors related to autism, <ref> White, John F. (2003) "Intestinal Pathology in Autism" ''Experimental Biology and Medicine'', ''228'', pp. 639-649.</ref>, Reichelt's hypothesis is regarded as either incorrect, incomplete, or requiring further investigation.<ref name="elder">Elder, J., et al. 2006. "The Gluten-Free, Casein-Free Diet in Autism: Results of a Preliminary Double Blind Clinical Trial." Journal of Autism and Developmental Disorders 36:413-420. </ref>
+Given the role of polypeptide growth factors in controlling cell proliferation, abnormalities in growth factor signaling are the basis for a variety of [[disease]]s, including many types of [[cancer]].
 == Peptides are an important research tool ==
 Peptides have received prominence in [[molecular biology]] in recent times for several reasons:
-#Peptides allow researchers to generate antibodies in animals without the need to purify the protein of interest. The researcher can simply make antigenic peptides of sections of the protein.
+#Peptides allow researchers to generate [[antibody|antibodies]] in animals without the need to purify the protein of interest. The researcher can simply make [[antigen|antigenic]] peptides of sections of the protein.
 #Peptides have become instrumental in [[mass spectrometry]], allowing the identification of proteins of interest based on peptide masses and sequences.
 #Peptides have recently been used in the study of protein structure and function. For example, synthetic peptides can be used as probes to determine where protein-peptide interactions occur.
@@ Line 75: / Line 60: @@
 ==Peptide families==
-Below is a more detailed list of the major families of ribosomal peptides.
+Below is a more detailed list of the major families of ribosomal peptides:
-Vasopressin and oxytocin
+*Vasopressin and oxytocin
-* [[Vasopressin]]
+** [[Vasopressin]]
-* [[Oxytocin]]
+** [[Oxytocin]]
-The [[Tachykinin peptides]]
+*The [[Tachykinin peptides]]
-* [[Substance P]]
+** [[Substance P]]
-* [[Kassinin]]
+** [[Kassinin]]
-* [[Neurokinin A]]
+** [[Neurokinin A]]
-* [[Eledoisin]]
+** [[Eledoisin]]
-* [[Neurokinin B]]
+** [[Neurokinin B]]
-[[Vasoactive intestinal peptides]]
+*[[Vasoactive intestinal peptides]]
-* [[Vasoactive intestinal peptide|VIP]] ''Vasoactive intestinal peptide''
+** [[Vasoactive intestinal peptide|VIP]] (''Vasoactive intestinal peptide'')
-* [[PACAP]] ''[[Pituitary adenylate cyclase activating peptide]]''
+** [[PACAP]] (''[[Pituitary adenylate cyclase activating peptide]]'')
-* [[PHI 27]]
+** [[PHI 27]]
-* [[PHM 27]]
+** [[PHM 27]]
-* [[GHRH 1-24]] ''[[Growth hormone releasing hormone 1-24]]''
+** [[GHRH 1-24]] (''[[Growth hormone releasing hormone 1-24]]'')
-* [[Glucagon]]
+** [[Glucagon]]
-* [[Secretin]]
+** [[Secretin]]
-[[Pancreatic polypeptide-related peptides]]
+*[[Pancreatic polypeptide-related peptides]]
-* [[NPY]]
+** [[NPY]]
-* [[PYY]] ''[[Peptide YY]]''
+** [[PYY]] (''[[Peptide YY]]'')
-* [[Avian pancreatic polypeptide|APP]] ''[[Avian pancreatic polypeptide]]''
+** [[Avian pancreatic polypeptide|APP]] (''Avian pancreatic polypeptide'')
-* [[HPP]] ''[[Human pancreatic polypeptide]]''
+** [[HPP]] (''[[Human pancreatic polypeptide]]'')
-[[Opioid peptides]]
+*[[Opioid peptides]]
-* [[Proopiomelanocortin]] ([[POMC]]) Peptides
+** [[Proopiomelanocortin]] ([[POMC]]) Peptides
-* The [[Enkephalin pentapeptides]]
+** The [[Enkephalin pentapeptides]]
-* The [[Prodynorphin peptides]]
+** The [[Prodynorphin peptides]]
-Calcitonin peptides
+*Calcitonin peptides
-* [[Calcitonin]]
+** [[Calcitonin]]
-* [[Amylin]]
+** [[Amylin]]
-*[[AGG01]]
+** [[AGG01]]
 ==References==
-*Stryer, L. 1995. ''Biochemistry'', 4th edition. New York, NY: W.H. Freeman.
+* Cooper, G. M., and R. E. Hausman. 2004. ''The Cell: A Molecular Approach,'' 3rd edition. Washington, DC: ASM Press & Sunderland, MA: Sinauer Associates. ISBN 0878932143
+* Lodish, H., D. Baltimore, A. Berk, S. L. Zipursky, P. Matsudaira, and J. Darnell. 1996. ''Molecular Cell Biology.'' Oxford: W H Freeman and Company. ISBN 0716727110
-==External links==
+* Stryer, L. 1995. ''Biochemistry'', 4th edition. New York, NY: W.H. Freeman. ISBN 0716720094
-*[http://www.peptideresource.com Peptide Resource Page]
-{{credit|98760524}}
+{{credit7|Peptide|98760524|Peptide_bond|114918900|Peptide_hormone|106998489|Neuropeptide|114698110|Vasopressin|115077827|Opioid_peptide|108943902|Pituitary_gland|114583980}}
 [[Category:Life sciences]]
+[[Category:Biochemistry]]