Cysteine

Not to be confused with cytosine, cystine, cytisine, cytidine, or Sistine.
"Cys" redirects here. For other uses, see Cys (disambiguation).
l-Cysteine
Skeletal formula of L-cysteine
Names
IUPAC name
Cysteine
Other names
  • 2-Amino-3-sulfhydrylpropanoic acid
Identifiers
3D model (JSmol)
Abbreviations Cys, C
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.000.145 Edit this at Wikidata
EC Number
  • 200-158-2
E number E920 (glazing agents, ...)
KEGG
UNII
  • InChI=1S/C3H7NO2S/c4-2(1-7)3(5)6/h2,7H,1,4H2,(H,5,6) checkY
    Key: XUJNEKJLAYXESH-UHFFFAOYSA-N checkY
  • InChI=1/C3H7NO2S/c4-2(1-7)3(5)6/h2,7H,1,4H2,(H,5,6)/t2-/m0/s1
    Key: XUJNEKJLAYXESH-REOHCLBHBU
  • InChI=1/C3H7NO2S/c4-2(1-7)3(5)6/h2,7H,1,4H2,(H,5,6)
    Key: XUJNEKJLAYXESH-UHFFFAOYAC
  • C([C@@H](C(=O)O)N)S
  • Zwitterion: C([C@@H](C(=O)[O-])[NH3+])S
Properties[4]
C3H7NO2S
Molar mass 121.15 g·mol−1
Appearance white crystals or powder
Melting point 240 °C (464 °F; 513 K) decomposes
277g/L (at 25 °C)[1]
Solubility 1.5g/100g ethanol 19 °C [2]
Acidity (pKa) 1.71 (conjugate acid), 8.33 (thiol), 10.78[3]
+9.4° (H2O, c = 1.3)
Supplementary data page
Cysteine (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

Cysteine (/ˈsɪstɪiːn/;[5] symbol Cys or C[6]) is a semiessential[7] proteinogenic amino acid with the formula HOOC−CH(−NH2)−CH2−SH. The thiol side chain in cysteine enables the formation of disulfide bonds, and often participates in enzymatic reactions as a nucleophile. Cysteine is chiral, but both D and L-cysteine are found in nature. L‑Cysteine is a protein monomer in all biota, and D-cysteine acts as a signaling molecule in mammalian nervous systems.[8] Cysteine is named after its discovery in urine, which comes from the urinary bladder or cyst, from Greek κύστις kýstis, "bladder".[9]

The thiol is susceptible to oxidation to give the disulfide derivative cystine, which serves an important structural role in many proteins. In this case, the symbol Cyx is sometimes used.[10][11] The deprotonated form can generally be described by the symbol Cym as well.[11][12]

When used as a food additive, cysteine has the E number E920.

Cysteine is encoded by the codons UGU and UGC.

Structure

Like other amino acids (not as a residue of a protein), cysteine exists as a zwitterion. Cysteine has l chirality in the older d/l notation based on homology to d- and l-glyceraldehyde. In the newer R/S system of designating chirality, based on the atomic numbers of atoms near the asymmetric carbon, cysteine (and selenocysteine) have R chirality, because of the presence of sulfur (or selenium) as a second neighbor to the asymmetric carbon atom. The remaining chiral amino acids, having lighter atoms in that position, have S chirality. Replacing sulfur with selenium gives selenocysteine.

(R)-Cysteine (left) and (S)-Cysteine (right) in zwitterionic form at neutral pH

Dietary sources

Cysteinyl is a residue in high-protein foods. Some foods considered rich in cysteine include poultry, eggs, beef, and whole grains. In high-protein diets, cysteine may be partially responsible for reduced blood pressure and stroke risk.[13] Although classified as a nonessential amino acid,[14] in rare cases, cysteine may be essential for infants, the elderly, and individuals with certain metabolic diseases or who suffer from malabsorption syndromes. Cysteine can usually be synthesized by the human body under normal physiological conditions if a sufficient quantity of methionine is available.

Industrial sources

The majority of l-cysteine is obtained industrially by hydrolysis of animal materials, such as poultry feathers or hog hair. Despite widespread rumor,[15] human hair is rarely a source material.[16] Indeed, food additive or cosmetic product manufactures may not legally source from human hair in the European Union.[17][18]

Some animal-originating sources of l-cysteine as a food additive contravene kosher, halal, vegan, or vegetarian diets.[15] To avoid this problem, synthetic l-cysteine, compliant with Jewish kosher and Muslim halal laws, is also available, albeit at a higher price.[19] The typical synthetic route involves fermentation with an artificial E. coli strain.[20]

Alternatively, Evonik (formerly Degussa) introduced a route from substituted thiazolines.[21] Pseudomonas thiazolinophilum hydrolyzes racemic 2‑amino-Δ2‑thiazoline-4‑carboxylic acid to l‑cysteine.[20]

Biosynthesis

Cysteine synthesis: Cystathionine beta synthase catalyzes the upper reaction and cystathionine gamma-lyase catalyzes the lower reaction.

In animals, biosynthesis begins with the amino acid serine. The sulfur is derived from methionine, which is converted to homocysteine through the intermediate S-adenosylmethionine. Cystathionine beta-synthase then combines homocysteine and serine to form the asymmetrical thioether cystathionine. The enzyme cystathionine gamma-lyase converts the cystathionine into cysteine and alpha-ketobutyrate. In plants and bacteria, cysteine biosynthesis also starts from serine, which is converted to O-acetylserine by the enzyme serine transacetylase. The enzyme cysteine synthase, using sulfide sources, converts this ester into cysteine, releasing acetate.[22]

Biological functions

The cysteine sulfhydryl group is nucleophilic and easily oxidized. The reactivity is enhanced when the thiol is ionized, and cysteine residues in proteins have pKa values close to neutrality, so are often in their reactive thiolate form in the cell.[23] Because of its high reactivity, the sulfhydryl group of cysteine has numerous biological functions.

Precursor to the antioxidant glutathione

Due to the ability of thiols to undergo redox reactions, cysteine and cysteinyl residues have antioxidant properties. Its antioxidant properties are typically expressed in the tripeptide glutathione, which occurs in humans and other organisms. The systemic availability of oral glutathione (GSH) is negligible; so it must be biosynthesized from its constituent amino acids, cysteine, glycine, and glutamic acid. While glutamic acid is usually sufficient because amino acid nitrogen is recycled through glutamate as an intermediary, dietary cysteine and glycine supplementation can improve synthesis of glutathione.[24]

Precursor to iron-sulfur clusters

Cysteine is an important source of sulfide in human metabolism. The sulfide in iron-sulfur clusters and in nitrogenase is extracted from cysteine, which is converted to alanine in the process.[25]

Metal ion binding

Beyond the iron-sulfur proteins, many other metal cofactors in enzymes are bound to the thiolate substituent of cysteinyl residues. Examples include zinc in zinc fingers and alcohol dehydrogenase, copper in the blue copper proteins, iron in cytochrome P450, and nickel in the [NiFe]-hydrogenases.[26] The sulfhydryl group also has a high affinity for heavy metals, so that proteins containing cysteine, such as metallothionein, will bind metals such as mercury, lead, and cadmium tightly.[27]

Roles in protein structure

In the translation of messenger RNA molecules to produce polypeptides, cysteine is coded for by the UGU and UGC codons.

Cysteine has traditionally been considered to be a hydrophilic amino acid, based largely on the chemical parallel between its sulfhydryl group and the hydroxyl groups in the side chains of other polar amino acids. However, the cysteine side chain has been shown to stabilize hydrophobic interactions in micelles to a greater degree than the side chain in the nonpolar amino acid glycine and the polar amino acid serine.[28] In a statistical analysis of the frequency with which amino acids appear in various proteins, cysteine residues were found to associate with hydrophobic regions of proteins. Their hydrophobic tendency was equivalent to that of known nonpolar amino acids such as methionine and tyrosine (tyrosine is polar aromatic but also hydrophobic[29]), those of which were much greater than that of known polar amino acids such as serine and threonine.[30] Hydrophobicity scales, which rank amino acids from most hydrophobic to most hydrophilic, consistently place cysteine towards the hydrophobic end of the spectrum, even when they are based on methods that are not influenced by the tendency of cysteines to form disulfide bonds in proteins. Therefore, cysteine is now often grouped among the hydrophobic amino acids,[31][32] though it is sometimes also classified as slightly polar,[33] or polar.[7]

Most cysteine residues are covalently bonded to other cysteine residues to form disulfide bonds, which play an important role in the folding and stability of some proteins, usually proteins secreted to the extracellular medium.[34] Since most cellular compartments are reducing environments, disulfide bonds are generally unstable in the cytosol with some exceptions as noted below.

Figure 2: Cystine (shown here in its neutral form), two cysteines bound together by a disulfide bond

Disulfide bonds in proteins are formed by oxidation of the sulfhydryl group of cysteine residues. The other sulfur-containing amino acid, methionine, cannot form disulfide bonds. More aggressive oxidants convert cysteine to the corresponding sulfinic acid and sulfonic acid. Cysteine residues play a valuable role by crosslinking proteins, which increases the rigidity of proteins and also functions to confer proteolytic resistance (since protein export is a costly process, minimizing its necessity is advantageous). Inside the cell, disulfide bridges between cysteine residues within a polypeptide support the protein's tertiary structure. Insulin is an example of a protein with cystine crosslinking, wherein two separate peptide chains are connected by a pair of disulfide bonds.

Protein disulfide isomerases catalyze the proper formation of disulfide bonds; the cell transfers dehydroascorbic acid to the endoplasmic reticulum, which oxidizes the environment. In this environment, cysteines are, in general, oxidized to cystine and are no longer functional as a nucleophiles.

Aside from its oxidation to cystine, cysteine participates in numerous post-translational modifications. The nucleophilic sulfhydryl group allows cysteine to conjugate to other groups, e.g., in prenylation. Ubiquitin ligases transfer ubiquitin to its pendant, proteins, and caspases, which engage in proteolysis in the apoptotic cycle. Inteins often function with the help of a catalytic cysteine. These roles are typically limited to the intracellular milieu, where the environment is reducing, and cysteine is not oxidized to cystine.

Evolutionary role of cysteine

Cysteine is considered a "newcomer" amino acid, being the 17th amino acid incorporated into the genetic code.[35][36] Similar to other later-added amino acids such as methionine, tyrosine, and tryptophan, cysteine exhibits strong nucleophilic and redox-active properties.[37][38] These properties contribute to the depletion of cysteine from respiratory chain complexes, such as Complexes I and IV,[39] since reactive oxygen species (ROS) produced by the respiratory chain can react with the cysteine residues in these complexes, leading to dysfunctional proteins and potentially contributing to aging. The primary response of a protein to ROS is the oxidation of cysteine and the loss of free thiol groups,[40] resulting in increased thiyl radicals and associated protein cross-linking.[41][42] In contrast, another sulfur-containing, redox-active amino acid, methionine, does not exhibit these biochemical properties and its content is relatively upregulated in mitochondrially encoded proteins.[43]

Applications

Cysteine, mainly the l-enantiomer, is a precursor in the food, pharmaceutical, and personal-care industries. One of the largest applications is the production of flavors. For example, the reaction of cysteine with sugars in a Maillard reaction yields meat flavors.[44] l-Cysteine is also used as a processing aid for baking.[45]

In the field of personal care, cysteine is used for permanent-wave applications, predominantly in Asia. Again, the cysteine is used for breaking up the disulfide bonds in the hair's keratin.

Cysteine is a very popular target for site-directed labeling experiments to investigate biomolecular structure and dynamics. Maleimides selectively attach to cysteine using a covalent Michael addition. Site-directed spin labeling for EPR or paramagnetic relaxation-enhanced NMR also uses cysteine extensively.

Reducing toxic effects of alcohol

Cysteine has been proposed as a preventive or antidote for some of the negative effects of alcohol, including liver damage and hangover. It counteracts the poisonous effects of acetaldehyde.[46] It binds to acetaldehyde to form the low-toxicity heterocycle methylthioproline.[47]

In a rat study, test animals received an LD90 dose of acetaldehyde. Those that received cysteine had an 80% survival rate; when both cysteine and thiamine were administered, all animals survived. The control group had a 10% survival rate.[48]

In 2020 an article was published that suggests L-cysteine might also work in humans.[49]

N-Acetylcysteine

N-Acetyl-l-cysteine is a derivative of cysteine wherein an acetyl group is attached to the nitrogen atom. This compound is sold as a dietary supplement, and used as an antidote in cases of acetaminophen overdose.[50]

Sheep

Cysteine is required by sheep to produce wool. It is an essential amino acid that is taken in from their feed. As a consequence, during drought conditions, sheep produce less wool; however, transgenic sheep that can make their own cysteine have been developed.[51]

Chemical reactions

Being multifunctional, cysteine undergoes a variety of reactions. Much attention has focused on protecting the sulfhydryl group.[52] Methylation of cysteine gives S-methylcysteine. Treatment with formaldehyde gives the thiazolidine thioproline. Cysteine forms a variety of coordination complexes upon treatment with metal ions.[53]

Safety

Relative to most other amino acids, cysteine is much more toxic.[54]

History

Main article: Cystine

In 1884 German chemist Eugen Baumann found that when cystine was treated with a reducing agent, cystine revealed itself to be a dimer of a monomer which he named "cysteïne".[55]

See also

Wikimedia Commons has media related to Cysteine.

References

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  55. ^ Baumann, E. (1884). "Ueber Cystin und Cysteïn" [On cystine and cysteine]. Zeitschrift für physiologische Chemie (in German). 8: 299–305. From pp. 301-302: "Die Analyse der Substanz ergibt Werthe, welche den vom Cystin (C6H12N2S2O4) verlangten sich nähern, […] nenne ich dieses Reduktionsprodukt des Cystins: Cysteïn." (Analysis of the substance [cysteine] reveals values which approximate those [that are] required by cystine (C6H12N2S2O4), however the new base [cysteine] can clearly be recognized as a reduction product of cystine, to which the [empirical] formula C3H7NSO2, [which had] previously [been] ascribed to cystine, is [now] ascribed. In order to indicate the relationships of this substance to cystine, I name this reduction product of cystine: "cysteïne".) Note: Baumann's proposed structures for cysteine and cystine (see p.302) are incorrect: for cysteine, he proposed CH3CNH2(SH)COOH .

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Main articles: lists of figures in Germanic heroic legend and Beowulf This is a list of Beowulf characters. Beowulf is an Old English heroic epic poem. Its creation dates to between the 8th[1] and the 11th centuries, the only surviving manuscript dating to circa 1010.[2] At 3183 lines, it is notable for its length. It has reached national epic status in England (although its setting is Scandinavia, not the British Isles).[3] There are a great many characters in Beowul...

 

 

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Les accidents ou explosions groupés d'obus peuvent aussi être source d'une pollution importante, généralement largement diffusée par le souffle (ici train allemand de munition, touché lors de la Première Guerre mondiale). Le problème de la toxicité des munitions (militaires et de chasse) le plus étudié a d'abord été celui qui est induit par le plomb (cause de saturnisme et neurotoxique à très faible dose chez le fœtus et l'embryon), mais depuis quelques années une littératur...

 

 

Smolensk Voivodeship

Voivodeship of the Grand Duchy of Lithuania Smolensk VoivodeshipPalatinatus smolencensisWojewództwo smoleńskieVoivodeship of the Grand Duchy of Lithuania, later Polish–Lithuanian Commonwealth1508–1654 Coat of arms Smolensk Voivodeship in red. Voivodeship's borders did not change since the Union of Lublin.Vilnius Voivodeship in the Polish–Lithuanian CommonwealthCapitalSmolenskHistory • Established 1508• Third partition of the Polish–Lithuanian Commonwealth 1654 Pol...

Stingray Brava

Television channel Stingray BravaStingray Brava LogoCountryNetherlandsBroadcast areaEurope WorldwideHeadquartersAlmere, NetherlandsProgrammingPicture format1080i HDTV(downscaled to 16:9 576i for the SDTV feed)OwnershipOwnerStingray Group (since 2015)Sister channelsStingray DjazzStingray iConcertsStingray Lite TVHistoryLaunched2006; 18 years ago (2006) (Pan-European feed)1 July 2010; 13 years ago (2010-07-01) (Dutch feed)ReplacedCultuur 7 (Flanders)Closed1&#...

 

 

Dingess, West Virginia

Unincorporated community in West Virginia, United StatesDingess, West VirginiaUnincorporated communityDingess, West VirginiaShow map of West VirginiaDingess, West VirginiaShow map of the United StatesCoordinates: 37°52′20″N 82°10′29″W / 37.87222°N 82.17472°W / 37.87222; -82.17472CountryUnited StatesStateWest VirginiaCountyMingoElevation971 ft (296 m)Time zoneUTC-5 (Eastern (EST)) • Summer (DST)UTC-4 (EDT)ZIP code25671Area code(s)304 &...

 

 

Jonathan Maidana

Questa voce sull'argomento calciatori argentini è solo un abbozzo. Contribuisci a migliorarla secondo le convenzioni di Wikipedia. Segui i suggerimenti del progetto di riferimento. Jonathan Maidana Maidana al Metalist nel 2009 Nazionalità  Argentina Altezza 183 cm Peso 86 kg Calcio Ruolo Difensore Squadra svincolato Carriera Giovanili  Los Andes Squadre di club1 2004-2006 Los Andes37 (3)2006-2008 Boca Juniors44 (0)2008-2009 Metalist34 (0)2010→  Banfield...

The Saviour (El Greco)

Painting by El Greco The SaviourArtistEl GrecoYear1608-1614Mediumoil on canvasDimensions72 cm × 55 cm (28 in × 22 in)LocationMuseo del Prado, Madrid The Saviour (Spanish - El Salvador) is a 1608–1614 oil on canvas painting by El Greco, now in the Museo del Prado in Madrid, Spain. It shows Christ as the saviour of the world, represented by the globe beneath his left hand. It draws on the traditions of Byzantine art whilst also incorporating element...

 

 

Missal

Liturgical book For other uses, see Missal (disambiguation). The Missal, a 1902 portrait by John William Waterhouse A missal is a liturgical book containing instructions and texts necessary for the celebration of Mass throughout the liturgical year. Versions differ across liturgical tradition, period, and purpose, with some missals intended to enable a priest to celebrate Mass publicly and others for private and lay use. The texts of the most common Eucharistic liturgy in the world, the Catho...

 

 

Обухівський районний історико-краєзнавчий музей

Обухівський краєзнавчий музей імені Юрія Домотенка 50°06′38″ пн. ш. 30°37′38″ сх. д. / 50.11081725462892678° пн. ш. 30.62733026379289214° сх. д. / 50.11081725462892678; 30.62733026379289214Координати: 50°06′38″ пн. ш. 30°37′38″ сх. д. / 50.11081725462892678° пн. ш. 30.62733026379289214°...

Briosco

Brioscocomune Briosco – Veduta LocalizzazioneStato Italia Regione Lombardia Provincia Monza e Brianza AmministrazioneSindacoAntonio Verbicaro (Lega-centro-destra) dal 04-10-2021 TerritorioCoordinate45°43′N 9°14′E45°43′N, 9°14′E (Briosco) Altitudine271 m s.l.m. Superficie6,61 km² Abitanti6 080[1] (31-12-2021) Densità919,82 ab./km² FrazioniCapriano, Fornaci Comuni confinantiBesana in Brianza, Carate Brianza, Giussano, Inver...

 

 

Grand Prix F1 Amerika Serikat 2004

Artikel ini memerlukan pemutakhiran informasi. Harap perbarui artikel dengan menambahkan informasi terbaru yang tersedia. Grand Prix F1 Amerika Serikat 2004 merupakan balapan Formula 1 pada 20 Juni 2004 di Indianapolis Motor Speedway.[1] Lomba Pos No Pembalap Tim Lap Waktu/Tersingkir Grid Poin 1 1 Michael Schumacher Ferrari 73 1:40'29.914 2 10 2 2 Rubens Barrichello Ferrari 73 +2.950 detik 1 8 3 10 Takuma Sato BAR-Honda 73 +22.036 detik 3 6 4 7 Jarno Trulli Renault 73 +34.544 detik 20...

 

 

Luis Fuentes (footballer, born 1986)

Mexican footballer In this Spanish name, the first or paternal surname is Fuentes and the second or maternal family name is Vargas. Luis Fuentes Fuentes with UNAM in 2016Personal informationFull name Luis Fernando Fuentes VargasDate of birth (1986-09-14) 14 September 1986 (age 37)Place of birth Chetumal, Quintana Roo, MexicoHeight 1.72 m (5 ft 8 in)Position(s) Left-backYouth career2007 Pumas MorelosSenior career*Years Team Apps (Gls)2007–2018 UNAM 257 (6)2017 →...

The Rational Peasant: The Political Economy of Rural Society in Vietnam

The Rational Peasant: The Political Economy of Rural Society in Vietnam AuthorSamuel L. PopkinLanguageEnglishGenrePolitical SciencePublished1979PublisherUniversity of California PressPublication placeUnited StatesPages332ISBN9780520039544The Rational Peasant: The Political Economy of Rural Society in Vietnam is a non-fiction book by University of California, San Diego political scientist Samuel L. Popkin. Originally conceived to be a reflection on the Vietnam Revolution, the book introduces t...

 

 

Tsar Bomba

Most powerful nuclear weapon ever detonated (1961) Largest bomb redirects here. For the list of most powerful nuclear weapons, see List of most powerful nuclear weapons. For other uses, see Tsar Bomba (disambiguation). Tsar Bomba Ground-level view of detonation (source: Rosatom State Corporation Communications Department: Rosatom: 20-08-2020 public release)[1]TypeThermonuclearPlace of originSoviet UnionProduction historyDesignerYulii KharitonAndrei SakharovViktor AdamskyYuri...

 

 

نوكيا N75

يفتقر محتوى هذه المقالة إلى الاستشهاد بمصادر. فضلاً، ساهم في تطوير هذه المقالة من خلال إضافة مصادر موثوق بها. أي معلومات غير موثقة يمكن التشكيك بها وإزالتها. (مارس 2016) نوكيا N75معلومات عامةالنوع هاتف محمولالصانع نوكياالجيل BB5.0التوفر في السوق غير متوفر حالياأهم التواريختاري�...

銀色のオリンシス

この記事は検証可能な参考文献や出典が全く示されていないか、不十分です。 出典を追加して記事の信頼性向上にご協力ください。（このテンプレートの使い方）出典検索?: 銀色のオリンシス – ニュース · 書籍 · スカラー · CiNii · J-STAGE · NDL · dlib.jp · ジャパンサーチ · TWL (2015年6月) 銀色のオリンシス ジャンル ロボット ア�...

 

 

Government budget

Government document presenting the government's proposed revenues and spending for a fiscal year This article may need to be rewritten to comply with Wikipedia's quality standards. You can help. The talk page may contain suggestions. (June 2024) A government budget is a projection of the government's revenues and expenditure for a particular period, often referred to as a financial or fiscal year, which may or may not correspond with the calendar year. Government revenues mostly include taxes...

 

 

Jacques Le Roy Ladurie

Pour les autres membres de la famille, voir Famille Le Roy Ladurie. Jacques Le Roy Ladurie Jacques Le Roy Ladurie en 1942. Fonctions Député français 9 décembre 1958 – 9 octobre 1962(3 ans et 10 mois) Élection 30 novembre 1958 Circonscription 5e du Calvados Législature Ire (Cinquième République) Groupe politique IPAS Prédécesseur Circonscription créée Successeur André Halbout 5 juillet 1951 – 1er décembre 1955(4 ans, 4 mois et 26 jours) Élection 17 ...

St. Marys River (Florida–Georgia)

River in Florida and Georgia, United States Aerial photo of St. Marys River dividing border of Georgia (left) and Florida (right) from 26,000 feet altitudeSt. Marys River watershedLocation of mouthLocationCountryUnited StatesStateFlorida, GeorgiaPhysical characteristicsMouthAtlantic Ocean • coordinates30°43′23″N 81°29′41″W / 30.72306°N 81.49472°W / 30.72306; -81.49472Length236 mi (380 km) St. Marys River seen from Fort Clinch,...

 

 

Pierre Lescot

French painter This article may require copy editing for grammar. You can assist by editing it. (May 2024) (Learn how and when to remove this message) The Lescot Wing of the Palais du Louvre Pierre Lescot (c. 1515 – 10 September 1578) was a French architect active during the French Renaissance. His most notable works include the Fontaine des Innocents and the Lescot wing of the Louvre in Paris. He played an important role in introducing elements of classical architecture into French a...