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(New page: {{BioPsy}} <div> <!-- Here is a table of data; skip past it to edit the text. --> <!-- Submit {{:subst:chembox_simple_organic}} to get this template or go to [[:Template:Chembox simple org...)
 
 
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{{Chembox new
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| ImageFileL1 = Methionin - Methionine.svg
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| ImageSizeL1 = 120px
{| id="bioChemInfoBox" align="right" border="1" cellspacing="0" cellpadding="3" style="margin: 0 0 0 0.5em; background: #FFFFFF; border-collapse: collapse; border-color: #C0C090; width: 320px;"
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| ImageFileR1 = L-methionine-B-3D-balls.png
! {{chembox header}}| '''Methionine'''
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| ImageSizeR1 = 120px
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| IUPACName = (''S'')-2-amino-4-(methylsulfanyl)-butanoic acid
| style="width: 30%;" | [[IUPAC nomenclature|Systematic name]]
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| OtherNames =
| (''S'')-2-amino-4-(methylsulfanyl)-<br/>butanoic acid
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| Section1 = {{Chembox Identifiers
|-
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| Abbreviations = Met, M
| Abbreviations
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| CASNo = 63-68-3
| '''Met<br/>M'''
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| PubChem = 876
|-
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| SMILES = CSCC[C@H](N)C(O)=O}}
| [[Chemical formula]]
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| Section2 = {{Chembox Properties
| C<sub>5</sub>H<sub>11</sub>NO<sub>2</sub>S
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| C=5 |H=11 |N=1 |O=2 |S=1
|-
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| Appearance =
| [[Molecular mass]]
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| Density =
| 149.21 g mol<sup>-1</sup>
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| MeltingPt =
|-
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| BoilingPt =
| [[Melting point]]
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| Solubility = }}
| 281 °C
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| Section3 = {{Chembox Hazards
|-
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| MainHazards =
| [[Density]]
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| FlashPt =
| 1.340 g cm<sup>-3</sup>
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| Autoignition = }}
|-
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}}
| [[Isoelectric point]]
 
| 5.74
 
|-
 
| [[Acid dissociation constant|p''K''<sub>a</sub>]]
 
| 2.16<br/>9.08
 
|-
 
| [[CAS registry number|CAS number]]
 
| [63-68-3]
 
|-
 
| [[PubChem]]
 
| [http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=876 876]
 
|-
 
| [[EINECS number]]
 
| 200-562-9
 
|-
 
| {{chembox SMILES|value=CSCC[C@H](N)C(O)=O}}
 
|-
 
| align="center" colspan="2" | [[Image:L-methionine-skeletal.png|120px|Chemical structure of methionine]] [[Image:L-methionine-3D-sticks.png|120px|Chemical structure of methionine]] [[Image:Met-stick.png|Chemical structure of methionine]]
 
|-
 
| {{chembox header}} | <small>[[wikipedia:Chemical infobox|Disclaimer and references]]</small>
 
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</div>
 
   
'''Methionine''' is an [[Essential amino acid|essential]] [[nonpolar]] [[amino acid]], and a [[lipotropic]].
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'''Methionine''' ({{pron-en|mɛˈθaɪəˌnin, -nɪn}}; abbreviated as '''Met''' or '''M''')<ref>{{cite web | author=IUPAC-IUBMB Joint Commission on Biochemical Nomenclature | title=Nomenclature and Symbolism for Amino Acids and Peptides | work=Recommendations on Organic & Biochemical Nomenclature, Symbols & Terminology etc | url=http://www.chem.qmul.ac.uk/iupac/AminoAcid/ | accessdate=2007-05-17}}</ref> is an α-[[amino acid]] with the [[chemical formula]] HO<sub>2</sub>CCH(NH<sub>2</sub>)CH<sub>2</sub>CH<sub>2</sub>SCH<sub>3</sub>. This [[Essential amino acid|essential amino acid]] is classified as [[nonpolar]]. Together with [[cysteine]], methionine is one of two [[sulfur]]-containing proteinogenic amino acids. Its derivative [[S-adenosyl methionine]] (SAM) serves as a [[methyl]] donor. Methionine is an intermediate in the biosynthesis of cysteine, [[carnitine]], [[taurine]], [[lecithin]], [[phosphatidylcholine]], and other [[phospholipid]]s. Improper conversion of methionine can lead to [[atherosclerosis]].
   
Methionine and [[cysteine]] are the only [[sulfur]]-containing proteinogenic amino acids. The methionine derivative [[S-adenosyl methionine]] (SAM) serves as a [[methyl]] donor. Methionine plays a role in cysteine, [[carnitine]] and [[taurine]] synthesis by the [[transsulfuration pathway]], [[lecithin]] production, the synthesis of [[phosphatidylcholine]] and other [[phospholipid]]s. Improper conversion of methionine can lead to [[atherosclerosis]]. Methionine is a [[chelating agent]].
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Methionine is one of only two amino acids encoded by a single codon (AUG) in the standard [[genetic code]] ([[tryptophan]], encoded by UGG, is the other). The codon AUG is also significant, in that it carries the "Start" message for a [[ribosome]] that signals the initiation of protein [[Translation (biology)|translation]] from mRNA. As a consequence, methionine is incorporated into the N-terminal position of all [[protein]]s in [[eukaryote]]s and [[archaea]] during translation, although it is usually removed by [[post-translational modification]].
 
Methionine is one of only two amino acids encoded by a single codon (AUG) in the standard [[genetic code]] ([[tryptophan]], encoded by UGG, is the other). The codon AUG is also significant, in that it carries the "Start" message for a [[ribosome]] to begin protein translation from mRNA. As a consequence, methionine is incorporated into the N-terminal position of all [[protein]]s in [[eukaryote]]s and [[archaea]] during translation, although it is usually removed by post-translational modification. Methionine can also occur at other positions in the protein, but during the creation of amino acid chains, methionine is always created first.
 
 
High levels of methionine can be found in sesame seeds, brazil nuts, fish and meat and some seeds. Most fruit and vegetables contain very little, though peppers and spinach are the best sources.
 
   
 
== Biosynthesis ==
 
== Biosynthesis ==
Since methionine is an essential amino acid, it cannot be synthesized in humans. However, in plants and microorganisms, methionine is synthesized from [[aspartic acid]] and [[cysteine]]. First, aspartic acid is converted to [[β-aspartyl-semialdehyde]], an important intermediate in the biosynthesis of methionine, [[lysine]], and, [[threonine]]. Of homoserine by [[homoserine acyltransferase]], puts a good [[leaving group]] on homoserine allowing it to react with cysteine to produce [[cystathionine]]. Enzymatic cleavage of cystathionine yields homocysteine, which can then be methylated by [[folic acid|folates]] to give methionine. Both [[cystathionine-γ-synthase]] and [[cystathionine-β-lyase]] require [[Pyridoxal-phosphate|Pyridoxyl-5'-phosphate]] as a [[cofactor]], while [[homocysteine methyltransferase]] requires [[Cyanocobalamin|Vitamin B12]] as a cofactor.
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As an essential amino acid, methionine is not synthesized in humans, hence we must ingest methionine or methionine-containing proteins. In plants and microorganisms, methionine is synthesized via a pathway that uses both [[aspartic acid]] and [[cysteine]]. First, aspartic acid is converted via β-aspartyl-semialdehyde into homoserine, introducing the pair of contiguous methylene groups. Homoserine converts to ''O''-succinyl [[homoserine]], which then reacts with cysteine to produce [[cystathionine]], which is cleaved to yield [[homocysteine]]. Subsequent methylation of the [[thiol]] group by [[folic acid|folates]] affords methionine. Both [[cystathionine-γ-synthase]] and [[cystathionine-β-lyase]] require [[Pyridoxal-phosphate|Pyridoxyl-5'-phosphate]] as a [[cofactor]], whereas [[homocysteine methyltransferase]] requires [[Cyanocobalamin|Vitamin B12]] as a cofactor.<ref>Nelson, D. L.; Cox, M. M. "Lehninger, Principles of Biochemistry" 3rd Ed. Worth Publishing: New York, 2000. ISBN 1-57259-153-6.</ref>
  +
   
 
Enzymes involved in methionine biosynthesis:
 
Enzymes involved in methionine biosynthesis:
 
# [[aspartokinase]]
 
# [[aspartokinase]]
# [[B-aspartate semialdehyde dehydrogenase]]
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# β-aspartate semialdehyde [[dehydrogenase]]
# [[Homserine dehydrogenase]]
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# homoserine dehydrogenase
# [[homoserine acyltransferase]]
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# homoserine [[acyltransferase]]
# [[cystathionine-γ-synthase]]
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# cystathionine-γ-[[synthase]]
# [[cystathionine-β-lyase]]
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# cystathionine-β-[[lyase]]
 
# [[methionine synthase]] (in mammals, this step is performed by [[homocysteine methyltransferase]])
 
# [[methionine synthase]] (in mammals, this step is performed by [[homocysteine methyltransferase]])
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[[Image:Met biosynthesis.gif|left|500px]]
   
 
<br style="clear: both;" />
 
<br style="clear: both;" />
[[Image:Met_biosynthesis.gif|center]]
 
   
 
== Other biochemical pathways ==
 
== Other biochemical pathways ==
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Methionine is converted to [[S-adenosylmethionine]] (SAM) by (1) [[methionine adenosyltransferase]]. SAM serves as a methyl-donor in many (2) [[methyltransferase]] reactions and is converted to [[S-adenosylhomocysteine]] (SAH). (3) [[adenosylhomocysteinase]] converts SAH to [[homocysteine]].
 
Methionine is converted to [[S-adenosylmethionine]] (SAM) by (1) [[methionine adenosyltransferase]]. SAM serves as a methyl-donor in many (2) [[methyltransferase]] reactions and is converted to [[S-adenosylhomocysteine]] (SAH). (3) [[adenosylhomocysteinase]] converts SAH to [[homocysteine]].
   
There are two fates of [[homocysteine]]. First, methionine can be regenerated from homocysteine via (4) [[methionine synthase]]. It can also be remethylated using glycine betaine (NNN-trimethyl glycine) to methionine via the enzyme Betaine-homocysteine methyltransferase (E.C.2.1.1.5, BHMT). BHMT makes up to 1.5% of all the soluble protein of the liver, and recent evidence suggests that it may have a greater influence on methionine and homocysteine homeostasis than Methionine sythase. Alternatively, homocysteine can be converted to cysteine. (5) [[cystathionine-β-synthase]] (a PLP-dependent enzyme) combines homocysteine and serine to produce [[cystathionine]]. Instead of degrading [[cystathionine]] via [[cystathionine-β-lyase]] as in the biosynthetic pathway, cystathionine is broken down to [[cysteine]] and α-ketobutyrate via (6) [[cystathionine-γ-lyase]]. (7) [[α-ketoacid dehydrogenase]] converts α-ketobutyrate to [[propionyl-CoA]], which is metabolized to [[succinyl-CoA]] in a three-step process (see [[propionyl-CoA]] for pathway).
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There are two fates of [[homocysteine]]:
  +
* Methionine can be regenerated from homocysteine via (4) [[methionine synthase]]. It can also be remethylated using [[glycine betaine]] (NNN-trimethyl glycine) to methionine via the enzyme [[Betaine-homocysteine methyltransferase]] (E.C.2.1.1.5, BHMT). BHMT makes up to 1.5% of all the soluble protein of the liver, and recent evidence suggests that it may have a greater influence on methionine and homocysteine homeostasis than methionine synthase.
  +
* Homocysteine can be converted to cysteine. (5) [[Cystathionine-β-synthase]] (a PLP-dependent enzyme) combines homocysteine and serine to produce [[cystathionine]]. Instead of degrading [[cystathionine]] via [[cystathionine-β-lyase]], as in the biosynthetic pathway, cystathionine is broken down to [[cysteine]] and [[α-ketobutyrate]] via (6) [[cystathionine-γ-lyase]]. (7) [[α-ketoacid dehydrogenase]] converts α-ketobutyrate to [[propionyl-CoA]], which is metabolized to [[succinyl-CoA]] in a three-step process (see [[propionyl-CoA]] for pathway).
   
[[Image:Met_pathway.gif|center]]
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[[Image:Met pathway.gif|Fates of methionine|right|450px]]
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  +
==Synthesis==
  +
[[Racemic]] methionine can be synthesized from diethyl sodium phthalimidomalonate by alkylation with chloroethylmethylsulfide (ClCH<sub>2</sub>CH<sub>2</sub>SCH<sub>3</sub>) followed by hydrolysis and decarboxylation.<ref>{{OrgSynth | author = Barger, G.; Weichselbaum, T. E. | title = dl-Methionine | | collvol = 2 | collvolpages = 384 | year = 1943 | prep = CV2P0384}}</ref>
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==Dietary aspects==
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High levels of methionine can be found in sesame seeds, Brazil nuts, fish, meats, and some other plant seeds. {{Fact|date=August 2007}} Most fruits and vegetables contain very little of it; however, some have significant amounts, such as spinach, potatoes, and boiled corn.{{Fact|date=August 2007}} Most [[legume]]s, though high in protein, are also low in methionine. DL-methionine is sometimes added as an ingredient to [[pet food]]s.<ref>[http://www.yorkshire-terrier.com/dogfood.htm What's in your dog's food?]</ref> Methionine, cysteine, and soy protein heated in a small amount of water creates a meat-like aroma.
   
 
== See also ==
 
== See also ==
* [[Allantoin]]
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* [[Paracetamol#Prevention|Paradote]] - A Methionine-Paracetamol preparation that might prevent hepatotoxicity.
* [[Formylmethionine]]
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  +
  +
== References ==
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* British National Formulary 55, March 2008; ISBN 978 085369 776 3
  +
{{Reflist}}
   
 
==External links==
 
==External links==
 
* [http://www.hcusupport.com/diet.htm Foods containing methionine]
 
* [http://www.hcusupport.com/diet.htm Foods containing methionine]
 
* [http://www.compchemwiki.org/index.php?title=Methionine Computational Chemistry Wiki]
 
* [http://www.compchemwiki.org/index.php?title=Methionine Computational Chemistry Wiki]
{{ChemicalSources}}
 
   
 
{{AminoAcids}}
 
{{AminoAcids}}
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{{Antidotes}}
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[[Category:Amino acids]]
   
[[Category:Proteinogenic amino acids]]
 
[[Category:Sulfur amino acids]]
 
[[Category:Thioethers]]
 
[[Category:Essential amino acids]]
 
   
 
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[[ko:메티오닌]]
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[[pl:Metionina]]
 
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[[ru:Метионин]]
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[[uk:Метіонін]]
 
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[[zh:蛋氨酸]]
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{{enWP|Methionine}}
 
{{enWP|Methionine}}

Latest revision as of 17:34, November 28, 2008

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Template:Chembox Abbreviations
style="background: #F8EABA; text-align: center;" colspan="2" Methionine
Identifiers
CAS number 63-68-3
PubChem 876
SMILES CSCC[C@H](N)C(O)=O
Properties
Molecular formula C5H11NO2S
Molar mass 149.2 g mol-1
Hazards
style="background: #F8EABA; text-align: center;" colspan="2" Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references


Methionine (Template:Pron-en; abbreviated as Met or M)[1] is an α-amino acid with the chemical formula HO2CCH(NH2)CH2CH2SCH3. This essential amino acid is classified as nonpolar. Together with cysteine, methionine is one of two sulfur-containing proteinogenic amino acids. Its derivative S-adenosyl methionine (SAM) serves as a methyl donor. Methionine is an intermediate in the biosynthesis of cysteine, carnitine, taurine, lecithin, phosphatidylcholine, and other phospholipids. Improper conversion of methionine can lead to atherosclerosis.

Methionine is one of only two amino acids encoded by a single codon (AUG) in the standard genetic code (tryptophan, encoded by UGG, is the other). The codon AUG is also significant, in that it carries the "Start" message for a ribosome that signals the initiation of protein translation from mRNA. As a consequence, methionine is incorporated into the N-terminal position of all proteins in eukaryotes and archaea during translation, although it is usually removed by post-translational modification.

Biosynthesis Edit

As an essential amino acid, methionine is not synthesized in humans, hence we must ingest methionine or methionine-containing proteins. In plants and microorganisms, methionine is synthesized via a pathway that uses both aspartic acid and cysteine. First, aspartic acid is converted via β-aspartyl-semialdehyde into homoserine, introducing the pair of contiguous methylene groups. Homoserine converts to O-succinyl homoserine, which then reacts with cysteine to produce cystathionine, which is cleaved to yield homocysteine. Subsequent methylation of the thiol group by folates affords methionine. Both cystathionine-γ-synthase and cystathionine-β-lyase require Pyridoxyl-5'-phosphate as a cofactor, whereas homocysteine methyltransferase requires Vitamin B12 as a cofactor.[2]


Enzymes involved in methionine biosynthesis:

  1. aspartokinase
  2. β-aspartate semialdehyde dehydrogenase
  3. homoserine dehydrogenase
  4. homoserine acyltransferase
  5. cystathionine-γ-synthase
  6. cystathionine-β-lyase
  7. methionine synthase (in mammals, this step is performed by homocysteine methyltransferase)
Met biosynthesis


Other biochemical pathways Edit

Although mammals cannot synthesize methionine, they can still utilize it in a variety of biochemical pathways:

Methionine is converted to S-adenosylmethionine (SAM) by (1) methionine adenosyltransferase. SAM serves as a methyl-donor in many (2) methyltransferase reactions and is converted to S-adenosylhomocysteine (SAH). (3) adenosylhomocysteinase converts SAH to homocysteine.

There are two fates of homocysteine:

Met pathway

SynthesisEdit

Racemic methionine can be synthesized from diethyl sodium phthalimidomalonate by alkylation with chloroethylmethylsulfide (ClCH2CH2SCH3) followed by hydrolysis and decarboxylation.[3]

Dietary aspectsEdit

High levels of methionine can be found in sesame seeds, Brazil nuts, fish, meats, and some other plant seeds. [How to reference and link to summary or text] Most fruits and vegetables contain very little of it; however, some have significant amounts, such as spinach, potatoes, and boiled corn.[How to reference and link to summary or text] Most legumes, though high in protein, are also low in methionine. DL-methionine is sometimes added as an ingredient to pet foods.[4] Methionine, cysteine, and soy protein heated in a small amount of water creates a meat-like aroma.

See also Edit

  • Paradote - A Methionine-Paracetamol preparation that might prevent hepatotoxicity.


References Edit

  1. IUPAC-IUBMB Joint Commission on Biochemical Nomenclature. Nomenclature and Symbolism for Amino Acids and Peptides. Recommendations on Organic & Biochemical Nomenclature, Symbols & Terminology etc. URL accessed on 2007-05-17.
  2. Nelson, D. L.; Cox, M. M. "Lehninger, Principles of Biochemistry" 3rd Ed. Worth Publishing: New York, 2000. ISBN 1-57259-153-6.
  3. Template:OrgSynth
  4. What's in your dog's food?

External linksEdit


Amino acids

Alanine | Arginine | Asparagine | Aspartic acid | Cysteine | Glutamic acid | Glutamine | Glycine | Histidine | Isoleucine | Leucine | Lysine | Methionine | Phenylalanine | Proline | Serine | Threonine | Tryptophan | Tyrosine | Valine
Essential amino acid | Protein | Peptide | Genetic code
Template:Antidotes


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