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glutamic acid

  (glū-tăm'ĭk) pronunciation
n.

A nonessential amino acid, C5H9NO4, occurring widely in plant and animal tissue and proteins, and having monosodium glutamate as a salt.

[GLUT(EN) + AM(IDE) + –IC.]


 
 
Food and Nutrition: glutamic acid

A non-essential amino acid; it is acidic since it has two carboxylic acid groups; its amide is glutamine. See also monosodium glutamate.

 
Food and Fitness: glutamic acid

An amino acid, the salt (glutamate) of which functions as a transmitter of nerve impulses in many parts of the brain and some areas of the spinal cord. It is used as a flavour enhancer in various processed foods and, like its salt monosodium glutamate, it can provoke allergic reactions in some people. See also Chinese restaurant syndrome.

 
Dental Dictionary: glutamic acid

n

A nonessential amino acid occurring widely in a number of proteins. Preparations of glutamic acid are used as aids for digestion.

 

One of the nonessential amino acids, closely related to glutamine. The two constitute a substantial fraction of the amino acids in many proteins (10 – 20% in many cases and up to 45% in some plant proteins). An important metabolic intermediate as well as a neurotransmitter molecule in the central nervous system, glutamic acid finds uses in medicine and biochemical research. Its sodium salt is the food flavour enhancer monosodium glutamate (MSG).

For more information on glutamic acid, visit Britannica.com.

 

An amino acid, the salt (glutamate) of which functions as an ionotropic neurotransmitter. Glutamate is secreted in many areas of the brain and by some neurones in the spinal cord where its effects are generally excitatory.

 
Columbia Encyclopedia: glutamic acid
(glūtăm'ĭk) , organic compound, one of the 20 amino acids commonly found in animal proteins. Only the L-stereoisomer occurs in mammalian proteins. Like aspartic acid, glutamic acid has an acidic carboxyl group on its side chain which can serve as both an acceptor and a donor of ammonia, a compound toxic to the body. Once glutamic acid has coupled with ammonia, it is called glutamine and can as such safely transport ammonia to the liver, where the ammonia is eventually converted to urea for excretion by the kidneys. Free glutamic acid (that not incorporated into proteins) can also be converted reversibly to α-ketoglutaric acid, an intermediate in the Krebs cycle, and as such can be degraded to carbon dioxide and water, or transformed into sugars. The acidic side chain of glutamic acid confers one negative charge under most conditions to proteins in which this amino acid is found, thus increasing the water solubility of the protein. Monosodium glutamate (MSG), the monosodium salt of L-glutamic acid, is widely used as a condiment. The amino acid was isolated from wheat gluten in 1866 and chemically synthesized in 1890. It is not essential to the human diet, since it can be synthesized in the body from the common intermediate α-ketoglutaric acid.


 
Veterinary Dictionary: glutamic acid

A dibasic nonessential amino acid occurring in proteins. It is also an inhibitory neurotransmitter in the central nervous system. Its hydrochloride salt is used as a gastric acidifier. The monosodium salt (sodium glutamate; SMG) is used in treating encephalopathies associated with hepatic disease, and to enhance the flavor of foods and tobacco.


 
Wikipedia: glutamic acid

Chemical structure of Glutamic acid Chemical structure of the amino acid glutamate

Glutamic acid

Systematic (IUPAC) name
(2S)-2-aminopentanedioic acid
Identifiers
CAS number 56-86-0
PubChem         611
Chemical data
Formula C5H9NO4 
Molar mass 147.13 g/mol
SMILES N[C@@H](CCC(O)=O)C(O)=O
Complete data

Glutamic acid or glutamate (abbreviated as Glu or E; Glx or Z represents either glutamic acid or glutamine), is the protonated form of glutamate (the anion). Glutamate is one of the 20 proteinogenic amino acids. It is not among the essential amino acids. Its codons are GAA and GAG.

As its name indicates, glutamic acid has a carboxylic acid component to its side chain. At typical pH's, the amino group is protonated and one or both of the carboxylic groups will be ionized. At neutral pH all three groups are ionized, and the species has a charge of -1. The pKa value for glutamic acid is 4.1, which means that below this pH, the carboxylic acid groups are not ionized in more than half of the molecules.

Biosynthesis

Reactants Products Enzymes
Glutamine + H2O Glu + NH3 GLS, GLS2
NAcGlu + H2O Glu + Acetate (unknown)
α-ketoglutarate + NADPH + NH4+ Glu + NADP+ + H2O GLUD1, GLUD2
α-ketoglutarate + α-amino acid Glu + α-oxo acid transaminase
1-pyrroline-5-carboxylate + NAD+ + H2O Glu + NADH ALDH4A1
N-formimino-L-glutamate + FH4 Glu + 5-formimino-FH4 FTCD

Function

In metabolism

Glutamate is a key molecule in cellular metabolism. In humans, dietary proteins are broken down by digestion into amino acids, which serves as metabolic fuel for other functional roles in the body. A key process in amino acid degradation is transamination, in which the amino group of an amino acid is transferred to an α-ketoacid, typically catalysed by a transaminase. The reaction can be generalised as such:

R1-amino acid + R2-α-ketoacid R1-α-ketoacid + R2-amino acid

A very common α-ketoacid is α-ketoglutarate, an intermediate in the citric acid cycle. Transamination of α-ketoglutarate gives glutamate. The resulting α-ketoacid product is often a useful one as well, which can contribute as fuel or as a substrate for further metabolism processes. Examples are as follows:

alanine + α-ketoglutarate pyruvate + glutamate
aspartate + α-ketoglutarate oxaloacetate + glutamate

Both pyruvate and oxaloacetate are key components of cellular metabolism, contributing as substrates or intermediates in fundamental processes such as glycolysis, gluconeogenesis and also the citric acid cycle.

Glutamate also plays an important role in the body's disposal of excess or waste nitrogen. Glutamate undergoes deamination, an oxidative reaction catalysed by glutamate dehydrogenase, as follows:

glutamate + water + NAD+ → α-ketoglutarate + NADH + ammonia + H+

Ammonia (as ammonium) is then excreted predominantly as urea, synthesised in the liver. Transamination can thus be linked to deamination, effectively allowing nitrogen from the amine groups of amino acids to be removed, via glutamate as an intermediate, and finally excreted from the body in the form of urea.

As a neurotransmitter

Glutamate is the most abundant fast excitatory neurotransmitter in the mammalian nervous system. At chemical synapses, glutamate is stored in vesicles. Nerve impulses trigger release of glutamate from the pre-synaptic cell. In the opposing post-synaptic cell, glutamate receptors, such as the NMDA receptor, bind glutamate and are activated. Because of its role in synaptic plasticity, it is believed that glutamic acid is involved in cognitive functions like learning and memory in the brain.

Glutamate transporters[3] are found in neuronal and glial membranes. They rapidly remove glutamate from the extracellular space. In brain injury or disease, they can work in reverse and excess glutamate can accumulate outside cells. This process causes calcium ions to enter cells via NMDA receptor channels, leading to neuronal damage and eventual cell death, and is called excitotoxicity. The mechanisms of cell death include:

  • Damage to mitochondria from excessively high intracellular Ca2+[4].
  • Glu/Ca2+-mediated promotion of transcription factors for pro-apoptotic genes, or downregulation of transcription factors for anti-apoptotic genes.

Excitotoxicity due to glutamate occurs as part of the ischemic cascade and is associated with stroke and diseases like amyotrophic lateral sclerosis, lathyrism, and Alzheimer's disease.

Glutamic acid has been implicated in epileptic seizures. Microinjection of glutamic acid into neurons produces spontaneous depolarisations around one second apart, and this firing pattern is similar to what is known as paroxysmal depolarizing shift in epileptic attacks. This change in the resting membrane potential at seizure foci could cause spontaneous opening of voltage-activated calcium channels, leading to glutamic acid release and further depolarization.

Experimental techniques to detect glutamate in intact cells include using a genetically-engineered nanosensor[2]. The sensor is a fusion of a glutamate-binding protein and two fluorescent proteins. When glutamate binds, the fluorescence of the sensor under ultraviolet light changes by resonance between the two fluorophores. Introduction of the nanosensor into cells enables optical detection of the glutamate concentration. Synthetic analogs of glutamic acid that can be activated by ultraviolet light have also been described[6]. This method of rapidly uncaging by photostimulation is useful for mapping the connections between neurons, and understanding synapse function.

In brain nonsynaptic glutamatergic signaling circuits

Extracellular glutamate in Drosophila brains has been found to regulate postsynaptic glutamate receptor clustering, via a process involving receptor desensitization[7]. A gene expressed in glial cells actively transports glutamate into the extracellular space[7], while in the nucleus accumbens stimulating group II metabotropic glutamate receptors was found to reduce extracellular glutamate levels[8]. This raises the possibility that this extracellular glutamate plays an "endocrine-like" role as part of a larger homeostatic system.

GABA precursor

Glu also serves as the precursor for the synthesis of the inhibitory GABA in GABA-ergic neurons. This reaction is catalyzed by GAD, glutamic acid decarboxylase, which is most abundant in cerebellum and pancreas.

Stiff-man syndrome is a neurologic disorder caused by anti-GAD antibodies, leading to a decrease in GABA synthesis and therefore, impaired motor function such as muscle stiffness and spasm. Since the pancreas is also abundant for the enzyme GAD, a direct immunological destruction occurs in the pancreas and the patients will have diabetes mellitus.

Sources and absorption

Glutamic acid is present in a wide variety of foods and is responsible for one of the five basic tastes of the human sense of taste (umami), especially in its physiological form, the sodium salt of glutamate at neutral pH. Ninety-five percent of the dietary glutamate is metabolized by intestinal cells in a first pass [5].

Overall, glutamic acid is the single largest contributor to intestinal energy. As a source for umami, the sodium salt of glutamic acid, monosodium glutamate (MSG) is used as a food additive to enhance the flavor of foods, although an identical effect can be achieved by mixing and cooking together different ingredients rich in this amino acid and other umami substances as well.

Another source of MSG is fruits, vegetables and nuts that have been sprayed with Auxigro. Auxigro is a growth enhancer that contains 30% glutamic acid.

China-based Fufeng Group Limited is the largest producer of Glutamic Acid in the world, with capacity increasing to 300,000 tons at the end of 2006 from 180,000 tons during 2006, putting them at 25 - 30% of the Chinese market. Meihua is the second largest Chinese producer. Together, the top five producers have roughly 50% share in China. Chinese demand is roughly 1.1 million tons per year, while global demand, including China, is 1.7 million tons per year.

Pharmacology

The drug phencyclidine (more commonly known as PCP) antagonizes glutamic acid non-competitively at the NMDA receptor. For the same reasons, sub-anaesthetic doses of Ketamine have strong dissociative and hallucinogenic effects. Glutamate does not easily pass the blood brain barrier, but instead this transport is mediated by a high affinity transport system [1]. It can also be converted into glutamine.

References

In line

  1. ^ Transport of glutamate and other amino acids at the blood-brain barrier.Smith QR

Other

  1. Nelson DL and Cox MM. Lehninger Principles of Biochemistry, 4th edition.
  2. a  Image:Free_text.png Okumoto, S., et al. (2005). "Detection of glutamate release from neurons by genetically encoded surface-displayed FRET nanosensors". Proceedings of the National Academy of Sciences U.S.A 102 (24): 8740-8745. PMID 15939876.  Free text
  3. a  Molecular pharmacology of glutamate transporters, EAATs and VGLUTs. Brain Res Brain Res Rev. 2004 Jul; 45(3):250-65. PubMed
  4. a  Delayed increase of Ca2+ influx elicited by glutamate: role in neuronal death. Mol Pharmacol. 1989 Jul;36(1):106-12; PubMed
  5. a  Image:Free_text.png Reeds, P.J., et al. (2000). "Intestinal glutamate metabolism". Journal of Nutrition 130 (4s): 978S-982S. PMID 10736365. . Free text
  6.   Image:Free_text.png Corrie, J.E., et al. (1993). "Postsynaptic activation at the squid giant synapse by photolytic release of L-glutamate from a 'caged' L-glutamate". Journal of Physiology 465 (Jun): 1-8. PMID 7901400.  Free text
  7.   Augustin H, Grosjean Y, Chen K, Sheng Q, Featherstone DE (2007). "Nonvesicular release of glutamate by glial xCT transporters suppresses glutamate receptor clustering in vivo". Journal of Neuroscience 27 (1): 111-123. PMID 17202478. 
  8.   Zheng Xi, Baker DA, Shen H, Carson DS, Kalivas PW (2002). "Group II metabotropic glutamate receptors modulate extracellular glutamate in the nucleus accumbens". Journal of Pharmacology and Experimental Therapeutics 300 (1): 162-171. PMID 11752112. 



Major families of biochemicals
Peptides | Amino acids | Nucleic acids | Carbohydrates | Lipids | Terpenes | Carotenoids | Tetrapyrroles | Enzyme cofactors | Steroids | Flavonoids | Alkaloids | Polyketides | Glycosides
Analogues of nucleic acids: The 20 Common Amino Acids Analogues of nucleic acids:
Alanine (dp) | Arginine (dp) | Asparagine (dp) | Aspartic acid (dp) | Cysteine (dp) | Glutamic acid (dp) | Glutamine (dp) | Glycine (dp) | Histidine (dp) | Isoleucine (dp) | Leucine (dp) | Lysine (dp) | Methionine (dp) | Phenylalanine (dp) | Proline (dp) | Serine (dp) | Threonine (dp) | Tryptophan (dp) | Tyrosine (dp) | Valine (dp)

 
 

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Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved.  Read more
Food and Nutrition. A Dictionary of Food and Nutrition. Copyright © 1995, 2003, 2005 by A. E. Bender and D. A. Bender. All rights reserved.  Read more
Food and Fitness. Food and Fitness: A Dictionary of Diet and Exercise. Copyright © 1997, 2003 by Oxford University Press. All rights reserved.  Read more
Dental Dictionary. Mosby's Dental Dictionary. Copyright © 2004 by Elsevier, Inc. All rights reserved.  Read more
Britannica Concise Encyclopedia. Britannica Concise Encyclopedia. © 2006 Encyclopædia Britannica, Inc. All rights reserved.  Read more
Sports Science and Medicine. The Oxford Dictionary of Sports Science & Medicine. Copyright © Michael Kent 1998, 2006, 2007. All rights reserved.  Read more
Columbia Encyclopedia. The Columbia Electronic Encyclopedia, Sixth Edition Copyright © 2003, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/  Read more
Veterinary Dictionary. The Veterinary Dictionary. Copyright © 2007 by Elsevier. All rights reserved.  Read more
Wikipedia. This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Glutamic acid" Read more

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