Difference between revisions of "Histidine" - New World Encyclopedia
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| − | [[Image:Succinate Dehygrogenase 1YQ3 Haem group.png|thumb|right|The histidine bound [[heme]] group of [[succinate dehydrogenase]], an | + | [[Image:Succinate Dehygrogenase 1YQ3 Haem group.png|thumb|right|The histidine bound [[heme]] group of [[succinate dehydrogenase]], an electron carrier in the [[mitochondria]]l electron transfer chain. The large semi-transparent sphere indicates the location of the [[iron]] [[ion]]. .]] |
| − | '''Histidine''' is an α-[[amino acid]] that is common in many | + | '''Histidine''' is an α-[[amino acid]] that is common in many [[protein]]s and is essential in the human diet, at least in children. It is the precusor of [[histamine]] and important in the synthesis of [[purine]]s. Like [[argenine]] and [[lysine]], histidine is classified as a basic amino acid. However, histidine's side chain allows it to act as both a base and an acid, both donating and accepting [[proton]]s, which can be of considerable importance in its role as part of proteins. |
| − | The L-isomer of histidine, which is the only form that is involved in protein synthesis, is one of the 20 [[amino acid#standard amino acid|standard amino acids]] common in animal proteins and required for normal functioning in humans. Histidine is variously classified as a "conditionally essential" or "essential" amino acid. An [[amino acid#essential amino acid|essential amino acid]] is one that cannot be synthesized by the [[human body]] from other compounds through chemical reactions, or at a rate sufficient to meet the body's physiological needs, and thus has to be obtained from the diet. Infants are unable to effectively synthesize histidine, making it nutritionally essential for infants. Historically, it has been considered non-essential in adults, who can go for periods of time without it in the diet, but it | + | The L-isomer of histidine, which is the only form that is involved in protein synthesis, is one of the 20 [[amino acid#standard amino acid|standard amino acids]] common in animal proteins and required for normal functioning in humans. Histidine is variously classified as a "conditionally essential" or "essential" amino acid. An [[amino acid#essential amino acid|essential amino acid]] is one that cannot be synthesized by the [[human body]] from other compounds through chemical reactions, or at a rate sufficient to meet the body's physiological needs, and thus has to be obtained from the diet. Infants are unable to effectively synthesize histidine, making it nutritionally essential for infants. Historically, it has been considered non-essential in adults, who can go for periods of time without it in the diet, but today it is commonly considered essential for adults as well. |
Histidine three letter code is His, its one letter code is H, and its systematic name is 2-Amino-3-(1H-imidazol-4-yl)- | Histidine three letter code is His, its one letter code is H, and its systematic name is 2-Amino-3-(1H-imidazol-4-yl)- | ||
propanoic acid (IUPAC-IUB 1983). | propanoic acid (IUPAC-IUB 1983). | ||
| − | + | ==Structure== | |
| − | ==Structure | ||
In [[biochemistry]], the term [[amino acid]] is frequently used to refer specifically to ''alpha amino acids'': those amino acids in which the amino and carboxylate groups are attached to the same [[carbon]], the so-called α–carbon (alpha carbon). The general structure of these alpha amino acids is: | In [[biochemistry]], the term [[amino acid]] is frequently used to refer specifically to ''alpha amino acids'': those amino acids in which the amino and carboxylate groups are attached to the same [[carbon]], the so-called α–carbon (alpha carbon). The general structure of these alpha amino acids is: | ||
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Most amino acids occur in two possible optical isomers, called D and L. The L amino acids represent the vast majority of amino acids found in [[protein]]s. They are called proteinogenic amino acids. As the name "proteinogenic" (literally, protein building) suggests, these amino acid are encoded by the standard genetic code and participate in the process of protein synthesis. There are two enantiomers of histidine, D-histidine and L-histidine, but only the L-stereoisomer is involved in synthesis of [[mammal]]ian proteins. | Most amino acids occur in two possible optical isomers, called D and L. The L amino acids represent the vast majority of amino acids found in [[protein]]s. They are called proteinogenic amino acids. As the name "proteinogenic" (literally, protein building) suggests, these amino acid are encoded by the standard genetic code and participate in the process of protein synthesis. There are two enantiomers of histidine, D-histidine and L-histidine, but only the L-stereoisomer is involved in synthesis of [[mammal]]ian proteins. | ||
| − | Histidine's general chemical formula is C<sub>6</sub>H<sub>9</sub>N<sub>3</sub>O<sub>2</sub>(IUPAC-IUB 1983). | + | Histidine's general chemical formula is C<sub>6</sub>H<sub>9</sub>N<sub>3</sub>O<sub>2</sub>(IUPAC-IUB 1983). |
| − | + | [[Image:Imidazole_chemical_structure.png|left|thumb|300px|Chemical structure of imidazole]] | |
| + | Histidine has an imidazole side chain. Imidazole is a [[heterocyclic]], [[aromatic]] [[organic compound]]. (Heterocyclic compounds are organic compounds that contain a ring structure containing atoms in addition to [[carbon]], such as [[sulfur]], [[oxygen]] or [[nitrogen]], as part of the ring.) Imidazole refers to the parent compound C<sub>3</sub>H<sub>4</sub>N<sub>2</sub>, while imidazoles are a class of heterocycles with similar ring structure but varying substituents. This ring system is present in [[histidine]], and the related hormone [[histamine]]. Imidazole can act as a [[base (chemistry)|base]] and as a weak [[acid]]. Imidazole exists in two [[tautomer|tautomeric]] forms with the [[hydrogen]] [[atom]] moving between the two [[nitrogen]]s. | ||
| − | == | + | In even slightly acidic conditions, protonation of the [[nitrogen]] occurs, changing the properties of histidine and the polypeptide as a whole. It is used in many proteins as a regulatory mechanism, changing the conformation and behavior of the polypeptide in acidic regions such as the late endosome or lysosome, enforcing conformation change in [[enzyme]]s. |
| − | The amino acid is a precursor for [[histamine]] and [[carnosine]] biosynthesis. | + | |
| + | ==Chemical properties== | ||
| + | |||
| + | The [[imidazole]] side chains and the relatively neutral pKa of histidine (ca 6.0) mean that relatively small shifts in [[cell (biology)|cellular]] [[pH]] will change its charge. For this reason, this amino acid side chain finds its way into considerable use as a coordinating [[ligand]] in [[metalloprotein]]s, and also as a [[catalyst|catalytic]] site in certain [[enzyme]]s, such as aiding the catalytic functions of [[chymotrypsin]] (digestive enzyme) and those enzymes involved with [[metabolism]] of proteins and carbohydrates. | ||
| + | |||
| + | Essentially, the imidazole side chain has two nitrogens with different properties: One is bound to [[hydrogen]] and donates its lone pair to the aromatic ring and as such is slighty [[acidic]], whereas the other one donates only one electron pair to the ring so it has a free lone pair and is [[basic (chemistry)|basic]]. That is, because of its unique side chain, histidine can act as both an acid and a base, both donating and accepting protons. These properties are exploited in different ways in proteins. In [[catalytic triad]]s (three amino acid components found inside the active site of certain protease enzymes: serine, aspartate, and histidine), the basic nitrogen of histidine is used to abstract a proton from [[serine]], [[threonine]], or [[cysteine]] to activate it as a [[nucleophile]]. In a histidine proton shuttle, histidine is used to quickly shuttle protons; it can do this by abstracting a proton with its basic nitrogen to make a positively-charged intermediate and then use another molecule, a buffer, to extract the proton from its acidic nitrogen. In [[carbonic anhydrase]]s, a histidine proton shuttle is utilized to rapidly shuttle protons away from a zinc-bound water molecule to quickly regenerate the active form of the enzyme. | ||
| + | |||
| + | Histidine is a precursor for [[histamine]] and [[carnosine]] biosynthesis. | ||
[[Image:Histidine decarboxylase.svg|thumb|center|433px|Conversion of [[histidine]] to [[histamine]] by [[histidine decarboxylase]]]] | [[Image:Histidine decarboxylase.svg|thumb|center|433px|Conversion of [[histidine]] to [[histamine]] by [[histidine decarboxylase]]]] | ||
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==Sources== | ==Sources== | ||
| − | Histidine is found in [[ | + | Histidine is found in [[fruit]]s such as [[banana]]s and [[grape]]s, [[meat]] and [[poultry]], and [[milk]] and milk products. It is also found in root [[vegetable]]s and all green vegetables, though in lesser quantities. |
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==Additional images== | ==Additional images== | ||
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== External links == | == External links == | ||
| − | *[http://www.chem.qmul.ac.uk/iubmb/enzyme/reaction/AminoAcid/His1.html Histidine biosynthesis (early stages)] | + | *[http://www.chem.qmul.ac.uk/iubmb/enzyme/reaction/AminoAcid/His1.html Histidine biosynthesis (early stages)]. Retrieved June 26, 2007. |
| − | *[http://www.chem.qmul.ac.uk/iubmb/enzyme/reaction/AminoAcid/His2.html Histidine biosynthesis (later stages)] | + | *[http://www.chem.qmul.ac.uk/iubmb/enzyme/reaction/AminoAcid/His2.html Histidine biosynthesis (later stages)]. Retrieved June 26, 2007. |
| − | *[http://www.chem.qmul.ac.uk/iubmb/enzyme/reaction/AminoAcid/His3.html Histidine catabolism] | + | *[http://www.chem.qmul.ac.uk/iubmb/enzyme/reaction/AminoAcid/His3.html Histidine catabolism]. Retrieved June 26, 2007. |
| − | *[http://www.compchemwiki.org/index.php?title=Histidine Computational Chemistry Wiki] | + | *[http://www.compchemwiki.org/index.php?title=Histidine Computational Chemistry Wiki]. Retrieved June 26, 2007. |
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{{AminoAcids}} | {{AminoAcids}} | ||
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[[Category:Proteinogenic amino acids]] | [[Category:Proteinogenic amino acids]] | ||
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[[Category:Essential amino acids]] | [[Category:Essential amino acids]] | ||
| − | + | ||
| − | {{credit|138340299}} | + | {{credit|Histidine|138340299|Imidazole|138556757}} |
[[Category:Life sciences]] | [[Category:Life sciences]] | ||
Revision as of 00:41, 26 June 2007
 
| |
Histidine | |
| Systematic (IUPAC) name | |
| 2-amino-3-(3H-imidazol-4-yl)propanoic acid | |
| Identifiers | |
| CAS number | 71-00-1 |
| PubChem | 773 |
| Chemical data | |
| Formula | C6H9N3O2 |
| Mol. weight | 155.16 |
| SMILES | N[C@@H](Cc1[nH]cnc1)C(O)=O |
| Complete data | |
Histidine is an α-amino acid that is common in many proteins and is essential in the human diet, at least in children. It is the precusor of histamine and important in the synthesis of purines. Like argenine and lysine, histidine is classified as a basic amino acid. However, histidine's side chain allows it to act as both a base and an acid, both donating and accepting protons, which can be of considerable importance in its role as part of proteins.
The L-isomer of histidine, which is the only form that is involved in protein synthesis, is one of the 20 standard amino acids common in animal proteins and required for normal functioning in humans. Histidine is variously classified as a "conditionally essential" or "essential" amino acid. An essential amino acid is one that cannot be synthesized by the human body from other compounds through chemical reactions, or at a rate sufficient to meet the body's physiological needs, and thus has to be obtained from the diet. Infants are unable to effectively synthesize histidine, making it nutritionally essential for infants. Historically, it has been considered non-essential in adults, who can go for periods of time without it in the diet, but today it is commonly considered essential for adults as well.
Histidine three letter code is His, its one letter code is H, and its systematic name is 2-Amino-3-(1H-imidazol-4-yl)- propanoic acid (IUPAC-IUB 1983).
Structure
In biochemistry, the term amino acid is frequently used to refer specifically to alpha amino acids: those amino acids in which the amino and carboxylate groups are attached to the same carbon, the so-called α–carbon (alpha carbon). The general structure of these alpha amino acids is:
R
|
H2N-C-COOH
|
H
where R represents a side chain specific to each amino acid. The exception to this basic structure is proline, whose side chain cyclizes onto the backbone, forming a ring structure in which a secondary amino group replaces the primary amino group.
Most amino acids occur in two possible optical isomers, called D and L. The L amino acids represent the vast majority of amino acids found in proteins. They are called proteinogenic amino acids. As the name "proteinogenic" (literally, protein building) suggests, these amino acid are encoded by the standard genetic code and participate in the process of protein synthesis. There are two enantiomers of histidine, D-histidine and L-histidine, but only the L-stereoisomer is involved in synthesis of mammalian proteins.
Histidine's general chemical formula is C6H9N3O2(IUPAC-IUB 1983).
Histidine has an imidazole side chain. Imidazole is a heterocyclic, aromatic organic compound. (Heterocyclic compounds are organic compounds that contain a ring structure containing atoms in addition to carbon, such as sulfur, oxygen or nitrogen, as part of the ring.) Imidazole refers to the parent compound C3H4N2, while imidazoles are a class of heterocycles with similar ring structure but varying substituents. This ring system is present in histidine, and the related hormone histamine. Imidazole can act as a base and as a weak acid. Imidazole exists in two tautomeric forms with the hydrogen atom moving between the two nitrogens.
In even slightly acidic conditions, protonation of the nitrogen occurs, changing the properties of histidine and the polypeptide as a whole. It is used in many proteins as a regulatory mechanism, changing the conformation and behavior of the polypeptide in acidic regions such as the late endosome or lysosome, enforcing conformation change in enzymes.
Chemical properties
The imidazole side chains and the relatively neutral pKa of histidine (ca 6.0) mean that relatively small shifts in cellular pH will change its charge. For this reason, this amino acid side chain finds its way into considerable use as a coordinating ligand in metalloproteins, and also as a catalytic site in certain enzymes, such as aiding the catalytic functions of chymotrypsin (digestive enzyme) and those enzymes involved with metabolism of proteins and carbohydrates.
Essentially, the imidazole side chain has two nitrogens with different properties: One is bound to hydrogen and donates its lone pair to the aromatic ring and as such is slighty acidic, whereas the other one donates only one electron pair to the ring so it has a free lone pair and is basic. That is, because of its unique side chain, histidine can act as both an acid and a base, both donating and accepting protons. These properties are exploited in different ways in proteins. In catalytic triads (three amino acid components found inside the active site of certain protease enzymes: serine, aspartate, and histidine), the basic nitrogen of histidine is used to abstract a proton from serine, threonine, or cysteine to activate it as a nucleophile. In a histidine proton shuttle, histidine is used to quickly shuttle protons; it can do this by abstracting a proton with its basic nitrogen to make a positively-charged intermediate and then use another molecule, a buffer, to extract the proton from its acidic nitrogen. In carbonic anhydrases, a histidine proton shuttle is utilized to rapidly shuttle protons away from a zinc-bound water molecule to quickly regenerate the active form of the enzyme.
Histidine is a precursor for histamine and carnosine biosynthesis.
The enzyme histidine ammonia-lyase converts histidine into ammonia and urocanic acid. A deficiency in this enzyme is present in the rare metabolic disorder histidinemia.
Sources
Histidine is found in fruits such as bananas and grapes, meat and poultry, and milk and milk products. It is also found in root vegetables and all green vegetables, though in lesser quantities.
Additional images
Histidine
ReferencesISBN links support NWE through referral fees
- Doolittle, R. F. 1989. Redundancies in protein sequences. In G. D. Fasman, ed., Prediction of Protein Structures and the Principles of Protein Conformation. New York: Plenum Press. ISBN 0306431319.
- International Union of Pure and Applied Chemistry and International Union of Biochemistry and Molecular Biology (IUPAC-IUB) Joint Commission on Biochemical Nomenclature. 1983. Nomenclature and symbolism for amino acids and peptides: Recommendations on organic & biochemical nomenclature, symbols & terminology. IUPAC-IUB. Retrieved June 14, 2007.
- Lehninger, A. L., D. L. Nelson, and M. M. Cox. 2000. Lehninger Principles of Biochemistry, 3rd ed. New York: Worth Publishing. ISBN 1572591536.
External links
- Histidine biosynthesis (early stages). Retrieved June 26, 2007.
- Histidine biosynthesis (later stages). Retrieved June 26, 2007.
- Histidine catabolism. Retrieved June 26, 2007.
- Computational Chemistry Wiki. Retrieved June 26, 2007.
| Major families of biochemicals | ||
| Peptides | Amino acids | Nucleic acids | Carbohydrates | Nucleotide sugars | 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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