L-histidine
   HOME

TheInfoList



OR:

Histidine (symbol His or H) is an
essential amino acid An essential amino acid, or indispensable amino acid, is an amino acid that cannot be synthesized from scratch by the organism fast enough to supply its demand, and must therefore come from the diet. Of the 21 amino acids common to all life forms ...
that is used in the biosynthesis of
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...
s. It contains an α-amino group (which is in the
protonated In chemistry, protonation (or hydronation) is the adding of a proton (or hydron, or hydrogen cation), usually denoted by H+, to an atom, molecule, or ion, forming a conjugate acid. (The complementary process, when a proton is removed from a Brà ...
–NH3+ form under biological conditions), a
carboxylic acid In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an Substituent, R-group. The general formula of a carboxylic acid is often written as or , sometimes as with R referring to an organyl ...
group (which is in the deprotonated –COO− form under biological conditions), and an
imidazole Imidazole (ImH) is an organic compound with the formula . It is a white or colourless solid that is soluble in water, producing a mildly alkaline solution. It can be classified as a heterocycle, specifically as a diazole. Many natural products, ...
side chain (which is partially protonated), classifying it as a positively charged amino acid at physiological pH. Initially thought essential only for infants, it has now been shown in longer-term studies to be essential for adults also. It is
encoded In communications and information processing, code is a system of rules to convert information—such as a letter, word, sound, image, or gesture—into another form, sometimes shortened or secret, for communication through a communication ...
by the
codons Genetic code is a set of rules used by living cells to translate information encoded within genetic material ( DNA or RNA sequences of nucleotide triplets or codons) into proteins. Translation is accomplished by the ribosome, which links pro ...
CAU and CAC. Histidine was first isolated by
Albrecht Kossel Ludwig Karl Martin Leonhard Albrecht Kossel (; 16 September 1853 – 5 July 1927) was a biochemist and pioneer in the study of genetics. He was awarded the Nobel Prize for Physiology or Medicine in 1910 for his work in determining the chemical ...
and
Sven Gustaf Hedin Sven Gustaf Hedin (6 October 1859 – 11 July 1933) was a Swedish chemist and physiologist credited with the discovery of histidine. He was born in Alseda parish, Jönköping County. He began his studies in 1878 and received his bachelor's degre ...
in 1896. The name stems from its discovery in tissue, from ''histós'' "tissue". It is also a
precursor Precursor or Precursors may refer to: *Precursor (religion), a forerunner, predecessor ** The Precursor, John the Baptist Science and technology * Precursor (bird), hypothesized genus of fossil birds that was composed of fossilized parts of unre ...
to
histamine Histamine is an organic nitrogenous compound involved in local immune responses communication, as well as regulating physiological functions in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus. Discovered in 19 ...
, a vital inflammatory agent in immune responses. The acyl
radical Radical (from Latin: ', root) may refer to: Politics and ideology Politics *Classical radicalism, the Radical Movement that began in late 18th century Britain and spread to continental Europe and Latin America in the 19th century *Radical politics ...
is histidyl.


Properties of the imidazole side chain

At neutral or
physiological pH Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a subdiscipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out chemical and ...
, the
imidazole Imidazole (ImH) is an organic compound with the formula . It is a white or colourless solid that is soluble in water, producing a mildly alkaline solution. It can be classified as a heterocycle, specifically as a diazole. Many natural products, ...
side chain In organic chemistry and biochemistry, a side chain is a substituent, chemical group that is attached to a core part of the molecule called the "main chain" or backbone chain, backbone. The side chain is a hydrocarbon branching element of a mo ...
is neutral. The
imidazole Imidazole (ImH) is an organic compound with the formula . It is a white or colourless solid that is soluble in water, producing a mildly alkaline solution. It can be classified as a heterocycle, specifically as a diazole. Many natural products, ...
side chain In organic chemistry and biochemistry, a side chain is a substituent, chemical group that is attached to a core part of the molecule called the "main chain" or backbone chain, backbone. The side chain is a hydrocarbon branching element of a mo ...
in histidine has a p''K''a of approximately 6.0. Thus, below a pH of 6, the imidazole ring is mostly
protonated In chemistry, protonation (or hydronation) is the adding of a proton (or hydron, or hydrogen cation), usually denoted by H+, to an atom, molecule, or ion, forming a conjugate acid. (The complementary process, when a proton is removed from a Brà ...
and carries a positive +1 charge (as described by the
Henderson–Hasselbalch equation In chemistry and biochemistry, the pH of weakly acidic Solution (chemistry), chemical solutions can be estimated using the Henderson-Hasselbach Equation: \ce = \ceK_\ce + \log_ \left( \frac \right) The equation relates the pH of the weak ac ...
). The resulting imidazolium ring bears two NH bonds and has a positive charge. The positive charge is equally distributed between both
nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...
s and can be represented with two equally important
resonance structure In chemistry, resonance, also called mesomerism, is a way of describing bonding in certain molecules or polyatomic ions by the combination of several contributing structures (or ''forms'', also variously known as ''resonance structures'' or '' ...
s. Sometimes, the symbol Hip is used for this protonated form instead of the usual His. Above pH 6, one of the two protons is lost. The remaining proton of the imidazole ring can reside on either nitrogen, giving rise to what are known as the N3-H or N1-H
tautomer In chemistry, tautomers () are structural isomers (constitutional isomers) of chemical compounds that readily interconvert. The chemical reaction interconverting the two is called tautomerization. This conversion commonly results from the reloca ...
s. In the N1-H tautomer, the NH is nearer the backbone. These neutral tautomers, also referred to as Nε (or Nτ, tau meaning ''tele'' — far) and Nδ (or Nπ, pi meaning ''pros'' — near), are sometimes referred to with symbols Hie and Hid, respectively. The imidazole/imidazolium ring of histidine is
aromatic In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated system, conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected from conjugati ...
at all pH values. Under certain conditions, all three ion-forming groups of histidine can be charged forming the histidinium cation. The acid-base properties of the imidazole side chain are relevant to the
catalytic mechanism Enzyme catalysis is the increase in the rate of a process by an "enzyme", a biological molecule. Most enzymes are proteins, and most such processes are chemical reactions. Within the enzyme, generally catalysis occurs at a localized site, calle ...
of many
enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...
s. In
catalytic triad A catalytic triad is a set of three coordinated amino acid residues that can be found in the active site of some enzymes. Catalytic triads are most commonly found in hydrolase and transferase enzymes (e.g. proteases, amidases, esterases, aminoac ...
s, the basic nitrogen of histidine abstracts a proton from
serine Serine (symbol Ser or S) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α- amino group (which is in the protonated − form under biological conditions), a carboxyl group (which is in the deprotonated − ...
,
threonine Threonine (symbol Thr or T) is an amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH form when dissolved in water), a carboxyl group (which is in the deprotonated −COO− ...
, or
cysteine Cysteine (; symbol Cys or C) is a semiessential proteinogenic amino acid with the chemical formula, formula . The thiol side chain in cysteine enables the formation of Disulfide, disulfide bonds, and often participates in enzymatic reactions as ...
to activate it as a
nucleophile In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are ...
. In a histidine
proton shuttle A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' (elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an electron (the proton ...
, 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 The carbonic anhydrases (or carbonate dehydratases) () form a family of enzymes that catalyst, catalyze the interconversion between carbon dioxide and water and the Dissociation (chemistry), dissociated ions of carbonic acid (i.e. bicarbonate a ...
s, a histidine proton shuttle is utilized to rapidly shuttle protons away from a
zinc Zinc is a chemical element; it has symbol Zn and atomic number 30. It is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic tabl ...
-bound water molecule to quickly regenerate the active form of the enzyme. In helices E and F of
hemoglobin Hemoglobin (haemoglobin, Hb or Hgb) is a protein containing iron that facilitates the transportation of oxygen in red blood cells. Almost all vertebrates contain hemoglobin, with the sole exception of the fish family Channichthyidae. Hemoglobin ...
, histidine influences binding of dioxygen as well as
carbon monoxide Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...
. This interaction enhances the affinity of Fe(II) for O2 but destabilizes the binding of CO, which binds only 200 times stronger in hemoglobin, compared to 20,000 times stronger in free
heme Heme (American English), or haem (Commonwealth English, both pronounced /Help:IPA/English, hi:m/ ), is a ring-shaped iron-containing molecule that commonly serves as a Ligand (biochemistry), ligand of various proteins, more notably as a Prostheti ...
. The tautomerism and acid-base properties of the imidazole side chain has been characterized by 15N NMR spectroscopy. The two 15N chemical shifts are similar (about 200 ppm, relative to
nitric acid Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...
on the sigma scale, on which increased shielding corresponds to increased
chemical shift In nuclear magnetic resonance (NMR) spectroscopy, the chemical shift is the resonant frequency of an atomic nucleus relative to a standard in a magnetic field. Often the position and number of chemical shifts are diagnostic of the structure of ...
).
NMR Nuclear magnetic resonance (NMR) is a physical phenomenon in which atomic nucleus, nuclei in a strong constant magnetic field are disturbed by a weak oscillating magnetic field (in the near and far field, near field) and respond by producing ...
spectral measurements shows that the chemical shift of N1-H drops slightly, whereas the chemical shift of N3-H drops considerably (about 190 vs. 145 ppm). This change indicates that the N1-H tautomer is preferred, possibly due to hydrogen bonding to the neighboring
ammonium Ammonium is a modified form of ammonia that has an extra hydrogen atom. It is a positively charged (cationic) polyatomic ion, molecular ion with the chemical formula or . It is formed by the protonation, addition of a proton (a hydrogen nucleu ...
. The shielding at N3 is substantially reduced due to the second-order
paramagnetic Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, ...
effect, which involves a symmetry-allowed interaction between the nitrogen lone pair and the excited π* states of the
aromatic ring In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected from conjugation alone. The e ...
. At pH > 9, the chemical shifts of N1 and N3 are approximately 185 and 170 ppm.


Ligand

Histidine forms complexes with many metal ions. The imidazole sidechain of the histidine residue commonly serves as a
ligand In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's el ...
in
metalloprotein Metalloprotein is a generic term for a protein that contains a metal ion cofactor. A large proportion of all proteins are part of this category. For instance, at least 1000 human proteins (out of ~20,000) contain zinc-binding protein domains al ...
s. One example is the axial base attached to Fe in myoglobin and hemoglobin. Poly-histidine tags (of six or more consecutive H residues) are utilized for protein purification by binding to columns with nickel or cobalt, with micromolar affinity. Natural poly-histidine peptides, found in the venom of the viper ''
Atheris squamigera ''Atheris squamigera'' (common names: green bush viper,David Mallow, Mallow D, David Ludwig (herpetologist), Ludwig D, Göran Nilson, Nilson G (2003). ''True Vipers: Natural History and Toxinology of Old World Vipers''. Malabar, Florida: Krieger ...
'' have been shown to bind Zn(II), Ni(II) and Cu(II) and affect the function of venom metalloproteases. N-terminal histidines are known to function as bidentate ligands, with a metal (generally copper) bound to both the amine of the
N-terminus The N-terminus (also known as the amino-terminus, NH2-terminus, N-terminal end or amine-terminus) is the start of a protein or polypeptide, referring to the free amine group (-NH2) located at the end of a polypeptide. Within a peptide, the amin ...
and the Nδ of the histidine; the Nε is often methylated. Although recently discovered, this "histidine brace" motif is critical in biogeochemical cycles: it functions as the active site of lytic polysaccharide monooxygenases (LPMOs), which break down unreactive polysaccharides such as cellulose. It is proposed that the evolution of these enzymes in fungi corresponds to the first widespread ability to decompose woody plant mass, leading to the end of the Carboniferous era and its mass accumulation of coal deposits.


Metabolism


Biosynthesis

-Histidine is an essential amino acid that is not synthesized ''
de novo De novo (Latin, , used in English to mean 'from the beginning', 'anew') may refer to: Science and computers * ''De novo'' mutation, a new germline mutation not inherited from either parent * ''De novo'' protein design, the creation of a protei ...
'' in humans. Humans and other animals must ingest histidine or histidine-containing proteins. The biosynthesis of histidine has been widely studied in prokaryotes such as ''E. coli''. Histidine synthesis in ''E. coli'' involves eight gene products (His1, 2, 3, 4, 5, 6, 7, and 8) and it occurs in ten steps. This is possible because a single gene product has the ability to catalyze more than one reaction. For example, as shown in the pathway, His4 catalyzes 4 different steps in the pathway. Histidine is synthesized from
phosphoribosyl pyrophosphate Phosphoribosyl pyrophosphate (PRPP) is a Sugar phosphates, pentose phosphate. It is a biochemical intermediate in the formation of purine nucleotides via Inosinic acid, inosine-5-monophosphate, as well as in pyrimidine nucleotide formation. Hence ...
(PRPP), which is made from
ribose-5-phosphate Ribose 5-phosphate (R5P) is both a product and an intermediate of the pentose phosphate pathway. The last step of the oxidative reactions in the pentose phosphate pathway is the production of ribulose 5-phosphate. Depending on the body's state, ...
by ribose-phosphate diphosphokinase in the
pentose phosphate pathway The pentose phosphate pathway (also called the phosphogluconate pathway and the hexose monophosphate shunt or HMP shunt) is a metabolic pathway parallel to glycolysis. It generates NADPH and pentoses (five-carbon sugars) as well as ribose 5-ph ...
. The first reaction of histidine biosynthesis is the condensation of PRPP and
adenosine triphosphate Adenosine triphosphate (ATP) is a nucleoside triphosphate that provides energy to drive and support many processes in living cell (biology), cells, such as muscle contraction, nerve impulse propagation, and chemical synthesis. Found in all known ...
(ATP) by the enzyme ATP-phosphoribosyl transferase. ATP-phosphoribosyl transferase is indicated by His1 in the image. His4 gene product then hydrolyzes the product of the condensation, phosphoribosyl-ATP, producing phosphoribosyl-AMP (PRAMP), which is an irreversible step. His4 then catalyzes the formation of phosphoribosylformiminoAICAR-phosphate, which is then converted to phosphoribulosylformimino-AICAR-P by the His6 gene product. His7 splits phosphoribulosylformimino-AICAR-P to form -erythro-imidazole-glycerol-phosphate. After, His3 forms imidazole acetol-phosphate releasing water. His5 then makes -histidinol-phosphate, which is then hydrolyzed by His2 making histidinol. His4 catalyzes the oxidation of -histidinol to form -histidinal, an amino aldehyde. In the last step, -histidinal is converted to -histidine. The histidine biosynthesis pathway has been studied in the fungus ''
Neurospora crassa ''Neurospora crassa'' is a type of red bread mold of the phylum Ascomycota. The genus name, meaning 'nerve spore' in Greek, refers to the characteristic striations on the spores. The first published account of this fungus was from an infestatio ...
'', and a gene (''His-3'') encoding a multienzyme complex was found that was similar to the ''His4'' gene of the bacterium ''
E. coli ''Escherichia coli'' ( )Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. is a gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escherichia'' that is commonly foun ...
''.Ahmed A. Organization of the histidine-3 region of Neurospora. Mol Gen Genet. 1968;103(2):185-93. doi: 10.1007/BF00427145. PMID 4306011 A genetic study of ''N. crassa'' histidine
mutant In biology, and especially in genetics, a mutant is an organism or a new genetic character arising or resulting from an instance of mutation, which is generally an alteration of the DNA sequence of the genome or chromosome of an organism. It i ...
s indicated that the individual activities of the multienzyme complex occur in discrete, contiguous sections of the ''His-3''
genetic map Genetic linkage is the tendency of DNA sequences that are close together on a chromosome to be inherited together during the meiosis phase of sexual reproduction. Two genetic markers that are physically near to each other are unlikely to be separ ...
, suggesting that the different activities of the multienzyme complex are encoded separately from each other. However, mutants were also found that lacked all three activities simultaneously, suggesting that some mutations cause loss of function of the complex as a whole. Like animals and microorganisms, plants need histidine for their growth and development. But unlike animals, microorganisms and plants can synthesize histidine. Both synthesize histidine from the biochemical intermediate phosphoribosyl pyrophosphate. In general, the histidine biosynthesis is very similar in plants and microorganisms.


Regulation of biosynthesis

This pathway requires energy in order to occur therefore, the presence of ATP activates the first enzyme of the pathway, ATP-phosphoribosyl transferase (shown as His1 in the image on the right). ATP-phosphoribosyl transferase is the rate determining enzyme, which is regulated through feedback inhibition meaning that it is inhibited in the presence of the product, histidine.


Degradation

Histidine can be metabolized into
glutamate Glutamic acid (symbol Glu or E; known as glutamate in its anionic form) is an α-amino acid that is used by almost all living beings in the biosynthesis of proteins. It is a Essential amino acid, non-essential nutrient for humans, meaning that ...
, which is readily metabolized into AKG ( alpha-ketoglutarate), making histidine one of the amino acids whose metabolites can become
citric acid cycle The citric acid cycle—also known as the Krebs cycle, Szent–Györgyi–Krebs cycle, or TCA cycle (tricarboxylic acid cycle)—is a series of chemical reaction, biochemical reactions that release the energy stored in nutrients through acetyl-Co ...
intermediates. The process requires several steps. In
prokaryote A prokaryote (; less commonly spelled procaryote) is a unicellular organism, single-celled organism whose cell (biology), cell lacks a cell nucleus, nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Ancient Gree ...
s, histidine first undergoes
deamination Deamination is the removal of an amino group from a molecule. Enzymes that catalysis, catalyse this reaction are called deaminases. In the human body, deamination takes place primarily in the liver; however, it can also occur in the kidney. In s ...
, the removal of its amino group by the emzyme histidase. This step produces ammonia and urocanic acid (urocanate). The enzyme urocanase then converts urocanic acid into imidazolonepropionate (4-imidazolone-5-propionate). The enzyme imidazolonepropionase then converts imidazolonepropionate into
formiminoglutamate Formiminoglutamic acid (FIGLU; conjugate base, formiminoglutamate) is an intermediate in the catabolism of L-histidine to L-glutamic acid. It thus is also a biomarker for intracellular levels of folate. The FIGLU test is used to identify vitami ...
(FIGLU). The enzyme
formimidoyltransferase cyclodeaminase Formimidoyltransferase cyclodeaminase or formiminotransferase cyclodeaminase (gene symbol FTCD in humans) is a bifunctional enzyme that catalyzes the following reactions: * conversion of formiminoglutamate and tetrahydrofolate into formiminot ...
removes the formimino group (which is transferred to
tetrahydrofolate Tetrahydrofolic acid (THFA), or tetrahydrofolate, is a folic acid derivative. Metabolism In humans, tetrahydrofolic acid is produced from dihydrofolic acid by dihydrofolate reductase. This reaction is inhibited by methotrexate. It is convert ...
), leaving behind a glutamate molecule. Glutamate can then be deaminated by
glutamate dehydrogenase Glutamate dehydrogenase (GLDH, GDH) is an enzyme observed in both prokaryotes and eukaryotic mitochondria. The aforementioned reaction also yields ammonia, which in eukaryotes is canonically processed as a substrate in the urea cycle. Typic ...
or transaminated to form α-ketoglutarate.


Conversion to other biologically active amines

* The histidine amino acid is a precursor for
histamine Histamine is an organic nitrogenous compound involved in local immune responses communication, as well as regulating physiological functions in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus. Discovered in 19 ...
, an amine produced in the body necessary for inflammation. * The enzyme
histidine ammonia-lyase Histidine ammonia-lyase (, histidase, histidinase) is an enzyme that in humans is encoded by the ''HAL'' gene. It converts histidine into ammonia and urocanic acid. Its systematic name is L-histidine ammonia-lyase (urocanate-forming). Function ...
converts histidine into
ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...
and
urocanic acid Urocanic acid (formally ''trans''-Urocanic acid) is an intermediate in the catabolism of L-histidine. The cis-urocanic acid, ''cis''-urocanic acid isomer is rare. Metabolism It is formed from L-histidine through the action of histidine ammonialyas ...
. A deficiency in this enzyme is present in the rare metabolic disorder
histidinemia Histidinemia is a rare autosomal recessive metabolic disorder caused by a deficiency of the enzyme histidase. Histidase is needed for the metabolism of the amino acid histidine. Although originally thought to be linked to multiple developmental ...
, producing
urocanic aciduria Urocanic aciduria is an autosomal recessive metabolic disorder caused by a deficiency of the enzyme urocanase. It is a secondary disorder of histidine metabolism.''Disorders of histidine metabolism.''http://www.ommbid.com/OMMBID/the_online_metabol ...
as a key diagnostic finding. * Histidine can be converted to 3-methylhistidine, which serves as a
biomarker In biomedical contexts, a biomarker, or biological marker, is a measurable indicator of some biological state or condition. Biomarkers are often measured and evaluated using blood, urine, or soft tissues to examine normal biological processes, ...
for skeletal muscle damage, by certain
methyltransferase Methyltransferases are a large group of enzymes that all methylate their substrates but can be split into several subclasses based on their structural features. The most common class of methyltransferases is class I, all of which contain a Ro ...
enzymes. * Histidine is also a precursor for
carnosine Carnosine (''beta''-alanyl-L-histidine) is a dipeptide molecule, made up of the amino acids beta-alanine and histidine. It is highly concentrated in muscle and brain tissues. Carnosine was discovered by Russian chemist Vladimir Gulevich. Ca ...
biosynthesis Biosynthesis, i.e., chemical synthesis occurring in biological contexts, is a term most often referring to multi-step, enzyme-Catalysis, catalyzed processes where chemical substances absorbed as nutrients (or previously converted through biosynthe ...
, which is a dipeptide found in skeletal muscle. * In
Actinomycetota The Actinomycetota (or Actinobacteria) are a diverse phylum of Gram-positive bacteria with high GC content. They can be terrestrial or aquatic. They are of great importance to land flora because of their contributions to soil systems. In soil t ...
and filamentous fungi, such as ''
Neurospora crassa ''Neurospora crassa'' is a type of red bread mold of the phylum Ascomycota. The genus name, meaning 'nerve spore' in Greek, refers to the characteristic striations on the spores. The first published account of this fungus was from an infestatio ...
'', histidine can be converted into the
antioxidant Antioxidants are Chemical compound, compounds that inhibit Redox, oxidation, a chemical reaction that can produce Radical (chemistry), free radicals. Autoxidation leads to degradation of organic compounds, including living matter. Antioxidants ...
ergothioneine Ergothioneine is a naturally occurring amino acid and is a thiourea derivative of histidine, containing a sulfur atom on the imidazole ring. This compound occurs in relatively few organisms, notably actinomycetota, cyanobacteria, and certain fun ...
.


Requirements

The
Food and Nutrition Board The Dietary Reference Intake (DRI) is a system of nutrition recommendations from the National Academy of Medicine (NAM) of the National Academies (United States). It was introduced in 1997 in order to broaden the existing guidelines known as Rec ...
(FNB) of the
U.S. Institute of Medicine The National Academy of Medicine (NAM), known as the Institute of Medicine (IoM) until 2015, is an American nonprofit, non-governmental organization. The National Academy of Medicine is a part of the National Academies of Sciences, Engineerin ...
set
Recommended Dietary Allowances In the U.S. and Canada, the Reference Daily Intake (RDI) is used in nutrition labeling on food and dietary supplement products to indicate the daily intake level of a nutrient that is considered to be sufficient to meet the requirements of 97†...
(RDAs) for
essential amino acid An essential amino acid, or indispensable amino acid, is an amino acid that cannot be synthesized from scratch by the organism fast enough to supply its demand, and must therefore come from the diet. Of the 21 amino acids common to all life forms ...
s in 2002. For histidine, for adults 19 years and older, 14 mg/kg body weight/day. Supplemental histidine is being investigated for use in a variety of different conditions, including neurological disorders, atopic dermatitis, metabolic syndrome, diabetes, uraemic anaemia, ulcers, inflammatory bowel diseases, malignancies, and muscle performance during strenuous exercise.


See also

* Carnosinemia * Beta-Alanine *
Diphthamide Diphthamide is a post-translationally modified histidine amino acid found in archaeal and eukaryotic elongation factor 2 (eEF-2). Dipthamide is named after the toxin produced by the bacterium ''Corynebacterium diphtheriae'', which targets diphth ...
*
Pauly reaction The Pauly reaction is a chemical test used for detecting the presence of tyrosine or histidine in proteins. It is named after German chemist Hermann Pauly, who first described the reaction. When proteins containing either tyrosine or histidine are ...


References


External links


Histidine MS Spectrum
{{Authority control Proteinogenic amino acids Alpha-Amino acids Basic amino acids Essential amino acids Imidazoles Carbonic anhydrase activators Aromatic amino acids