Cystine

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Cystine
Cystine-from-xtal-2D-skeletal.png
Cystine-from-xtal-Mercury-3D-balls-thin.png
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.000.270 OOjs UI icon edit-ltr-progressive.svg
KEGG
PubChem CID
UNII
  • InChI=1S/C6H12N2O4S2/c7-3(5(9)10)1-13-14-2-4(8)6(11)12/h3-4H,1-2,7-8H2,(H,9,10)(H,11,12) Yes check.svgY
    Key: LEVWYRKDKASIDU-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/C6H12N2O4S2/c7-3(5(9)10)1-13-14-2-4(8)6(11)12/h3-4H,1-2,7-8H2,(H,9,10)(H,11,12)
    Key: LEVWYRKDKASIDU-UHFFFAOYAA
  • C(C(C(=O)O)N)SSCC(C(=O)O)N
Properties
C6H12N2O4S2
Molar mass 240.29 g·mol−1
Hazards
Safety data sheet (SDS) External MSDS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Cystine is the oxidized derivative of the amino acid cysteine and has the formula (SCH2CH(NH2)CO2H)2. It is a white solid that is poorly soluble in water. As a residue in proteins, cystine serves two functions: a site of redox reactions and a mechanical linkage that allows proteins to retain their three-dimensional structure. [1]

Contents

Formation and reactions

Structure

Cystine is the disulfide derived from the amino acid cysteine. The conversion can be viewed as an oxidation:

2 HO2CCH(NH2)CH2SH + 0.5 O2 → (HO2CCH(NH2)CH2S)2 + H2O

Cystine contains a disulfide bond, two amine groups, and two carboxylic acid groups. As for other amino acids, the amine and carboxylic acid groups exist in rapid equilibrium with the ammonium-carboxylate tautomer. The great majority of the literature concerns the l,l-cystine, derived from l-cysteine. Other isomers include d,d-cystine and the meso isomer d,l-cystine, neither of which is biologically significant.

Occurrence

Cystine is common in many foods such as eggs, meat, dairy products, and whole grains as well as skin, horns and hair. It was not recognized as being derived of proteins until it was isolated from the horn of a cow in 1899. [2] Human hair and skin contain approximately 10–14% cystine by mass. [3]

History

Cystine was discovered in 1810 by the English chemist William Hyde Wollaston, who called it "cystic oxide". [4] In 1833, the Swedish chemist Jöns Jacob Berzelius named the amino acid "cystine". [5] The Norwegian chemist Christian J. Thaulow determined, in 1838, the empirical formula of cystine. [6] In 1884, the 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". [7] In 1899, cystine was first isolated from protein (horn tissue) by the Swedish chemist Karl A. H. Mörner (1855-1917). [8] The chemical structure of cystine was determined by synthesis in 1903 by the German chemist Emil Erlenmeyer. [9] [10] [11]

Redox

It is formed from the oxidation of two cysteine molecules, which results in the formation of a disulfide bond. In cell biology, cystine residues (found in proteins) only exist in non-reductive (oxidative) organelles, such as the secretory pathway (endoplasmic reticulum, Golgi apparatus, lysosomes, and vesicles) and extracellular spaces (e.g., extracellular matrix). Under reductive conditions (in the cytoplasm, nucleus, etc.) cysteine is predominant. The disulfide link is readily reduced to give the corresponding thiol cysteine. Typical thiols for this reaction are mercaptoethanol and dithiothreitol:

(SCH2CH(NH2)CO2H)2 + 2 RSH → 2 HSCH2CH(NH2)CO2H + RSSR

Because of the facility of the thiol-disulfide exchange, the nutritional benefits and sources of cystine are identical to those for the more-common cysteine. Disulfide bonds cleave more rapidly at higher temperatures. [12]

Cystine-based disorders

Comparison of different types of urinary crystals. Urine crystals comparison.png
Comparison of different types of urinary crystals.

The presence of cystine in urine is often indicative of amino acid reabsorption defects. Cystinuria has been reported to occur in dogs. [13] In humans the excretion of high levels of cystine crystals can be indicative of cystinosis, a rare genetic disease. Cystine stones account for about 1-2% of kidney stone disease in adults. [14] [15]

Biological transport

Cystine serves as a substrate for the cystine-glutamate antiporter. This transport system, which is highly specific for cystine and glutamate, increases the concentration of cystine inside the cell. In this system, the anionic form of cystine is transported in exchange for glutamate. Cystine is quickly reduced to cysteine.[ citation needed ] Cysteine prodrugs, e.g. acetylcysteine, induce release of glutamate into the extracellular space.

Nutritional supplements

Cysteine supplements are sometimes marketed as anti-aging products with claims of improved skin elasticity.[ citation needed ] Cysteine is more easily absorbed by the body than cystine, so most supplements contain cysteine rather than cystine. N-acetyl-cysteine (NAC) is better absorbed than other cysteine or cystine supplements.

See also

Related Research Articles

<span class="mw-page-title-main">Amino acid</span> Organic compounds containing amine and carboxylic groups

Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 appear in the genetic code of all life.

<span class="mw-page-title-main">Cysteine</span> Proteinogenic amino acid

Cysteine is a semiessential proteinogenic amino acid with the formula HOOC−CH(−NH2)−CH2−SH. The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile. Cysteine is chiral, only L-cysteine is found in nature.

<span class="mw-page-title-main">Arginine</span> Amino acid

Arginine is the amino acid with the formula (H2N)(HN)CN(H)(CH2)3CH(NH2)CO2H. The molecule features a guanidino group appended to a standard amino acid framework. At physiological pH, the carboxylic acid is deprotonated (−CO2−) and both the amino and guanidino groups are protonated, resulting in a cation. Only the l-arginine (symbol Arg or R) enantiomer is found naturally. Arg residues are common components of proteins. It is encoded by the codons CGU, CGC, CGA, CGG, AGA, and AGG. The guanidine group in arginine is the precursor for the biosynthesis of nitric oxide. Like all amino acids, it is a white, water-soluble solid.

Serine is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group, a carboxyl group, and a side chain consisting of a hydroxymethyl group, classifying it as a polar amino acid. It can be synthesized in the human body under normal physiological circumstances, making it a nonessential amino acid. It is encoded by the codons UCU, UCC, UCA, UCG, AGU and AGC.

In biochemistry, a disulfide refers to a functional group with the structure R−S−S−R′. The linkage is also called an SS-bond or sometimes a disulfide bridge and is usually derived by the coupling of two thiol groups. In biology, disulfide bridges formed between thiol groups in two cysteine residues are an important component of the secondary and tertiary structure of proteins. Persulfide usually refers to R−S−S−H compounds.

<span class="mw-page-title-main">Thiol</span> Any organic compound having a sulfanyl group (–SH)

In organic chemistry, a thiol, or thiol derivative, is any organosulfur compound of the form R−SH, where R represents an alkyl or other organic substituent. The −SH functional group itself is referred to as either a thiol group or a sulfhydryl group, or a sulfanyl group. Thiols are the sulfur analogue of alcohols, and the word is a blend of "thio-" with "alcohol".

<span class="mw-page-title-main">Post-translational modification</span> Biological processes

Post-translational modification (PTM) is the covalent process of changing proteins following protein biosynthesis. PTMs may involve enzymes or occur spontaneously. Proteins are created by ribosomes translating mRNA into polypeptide chains, which may then change to form the mature protein product. PTMs are important components in cell signalling, as for example when prohormones are converted to hormones.

<span class="mw-page-title-main">Lanthionine</span> Chemical compound

Lanthionine is a nonproteinogenic amino acid with the chemical formula (HOOC-CH(NH2)-CH2-S-CH2-CH(NH2)-COOH). It is typically formed by a cysteine residue and a dehydrated serine residue. Despite its name, lanthionine does not contain the element lanthanum.

<i>S</i>-Allylcysteine Chemical compound

S-Allylcysteine (SAC) is an organosulfur compound that has the formula HO2CCH(NH2)CH2SCH2C=CH2. It is the S-allylated derivative of the amino acid cysteine. As such only the L-enantiomer is significant biologically. SAC constituent of aged garlic. A number of related compounds are found in garlic, including the disulfide S-"allylmercaptocysteine" and γ-glutamyl-S-allylcysteine" (GSAC).

Cysteine metabolism refers to the biological pathways that consume or create cysteine. The pathways of different amino acids and other metabolites interweave and overlap to creating complex systems.

<span class="mw-page-title-main">Sulfur assimilation</span> Incorporation of sulfur into living organisms

Sulfur assimilation is the process by which living organisms incorporate sulfur into their biological molecules. In plants, sulfate is absorbed by the roots and then be transported to the chloroplasts by the transipration stream where the sulfur are reduced to sulfide with the help of a series of enzymatic reactions. Furthermore, the reduced sulfur is incorporated into cysteine, an amino acid that is a precursor to many other sulfur-containing compounds. In animals, sulfur assimilation occurs primarily through the diet, as animals cannot produce sulfur-containing compounds directly. Sulfur is incorporated into amino acids such as cysteine and methionine, which are used to build proteins and other important molecules. Besides, With the rapid development of economy, the increase emission of sulfur results in environmental issues, such as acid rain and hydrogen sulfilde.

<span class="mw-page-title-main">Amino acid synthesis</span> The set of biochemical processes by which amino acids are produced

Amino acid synthesis is the set of biochemical processes by which the amino acids are produced. The substrates for these processes are various compounds in the organism's diet or growth media. Not all organisms are able to synthesize all amino acids. For example, humans can synthesize 11 of the 20 standard amino acids. These 11 are called the non-essential amino acids).

<span class="mw-page-title-main">Erlenmeyer–Plöchl azlactone and amino-acid synthesis</span>

The Erlenmeyer–Plöchl azlactone and amino acid synthesis, named after Friedrich Gustav Carl Emil Erlenmeyer who partly discovered the reaction, is a series of chemical reactions which transform an N-acyl glycine to various other amino acids via an oxazolone.

<i>O</i>-Acetylserine Chemical compound

O-Acetylserine is an α-amino acid with the chemical formula HO2CCH(NH2)CH2OC(O)CH3. It is an intermediate in the biosynthesis of the common amino acid cysteine in bacteria and plants. O-Acetylserine is biosynthesized by acetylation of the serine by the enzyme serine transacetylase. The enzyme O-acetylserine (thiol)-lyase, using sulfide sources, converts this ester into cysteine, releasing acetate:

<span class="mw-page-title-main">Cystine/glutamate transporter</span> Protein found in humans

Cystine/glutamate transporter is an antiporter that in humans is encoded by the SLC7A11 gene.

<span class="mw-page-title-main">Glyceric acid</span> Chemical compound

Glyceric acid refers to organic compounds with the formula HOCH2CH(OH)CO2H. It occurs naturally and is classified as three-carbon sugar acid. It is chiral. Salts and esters of glyceric acid are known as glycerates.

<span class="mw-page-title-main">Non-proteinogenic amino acids</span> Are not naturally encoded in the genome

In biochemistry, non-coded or non-proteinogenic amino acids are distinct from the 22 proteinogenic amino acids which are naturally encoded in the genome of organisms for the assembly of proteins. However, over 140 non-proteinogenic amino acids occur naturally in proteins and thousands more may occur in nature or be synthesized in the laboratory. Chemically synthesized amino acids can be called unnatural amino acids. Unnatural amino acids can be synthetically prepared from their native analogs via modifications such as amine alkylation, side chain substitution, structural bond extension cyclization, and isosteric replacements within the amino acid backbone. Many non-proteinogenic amino acids are important:

<span class="mw-page-title-main">Selenocystine</span> Chemical compound

Selenocystine is the amino acid with the formula (HO2CCH CH2Se)2. It is the oxidized derivative of the canonical amino acid selenocysteine. The compound can also be prepared synthetically from serine. Because selenocysteine is not easily isolated or handled, it is often generated by reduction of selenocystine in situ. The selenium-selenium bond length is 2.321 Å, which is 14% longer than the disulfide bond in cystine at 2.040 Å.

<span class="mw-page-title-main">Tellurocysteine</span> Chemical compound

Tellurocysteine is an amino acid with the formula HTeCH2CH(NH2)CO2H. It would be the heavy analogue of serine, cysteine, and selenocysteine. Tellurol (RTeH) is a rare and fragile functional group, especially alkyl derivatives. Furthermore the C-Te bond is weak compared to 234 kJ/mol for the C-Se bond. These factors combine to make tellurocysteine very labile. Even selenocysteine occurs only rarely in nature. Instead of tellurocysteine, tellurocystine is generally isolated instead. It has the formula (TeCH2CH CO2H)2, with a central Te-Te bond.

<span class="mw-page-title-main">Chloroalanine</span> Chemical compound

Chloroalanine (3-chloroalanine) is an unnatural amino acid with the formula ClCH2CH(NH2)CO2H. It is a white, water-soluble solid. The compound is usually derived from chlorination of serine. The compound is used in the synthesis of other amino acids by replacement of the chloride. Protected forms of the related iodoalanine are also known.

References

  1. ↑ Nelson, D. L.; Cox, M. M. (2000) Lehninger, Principles of Biochemistry. 3rd Ed. Worth Publishing: New York. ISBN   1-57259-153-6.
  2. ↑ "cystine". Encyclopædia Britannica. 2007. Encyclopædia Britannica Online. 27 July 2007
  3. ↑ Gortner, R. A.; Hoffman, W. F. (1925). "l-Cystine". Organic Syntheses . 5: 39.
  4. ↑ Wollaston, William Hyde (1810). "On cystic oxide, a new species of urinary calculus". Philosophical Transactions of the Royal Society of London. 100: 223–230. On p. 227, Wollaston named cystine "cystic oxide".
  5. ↑ Berzelius, J.J.; Esslinger, Me., trans. (1833). Traité de Chimie (in French). Vol. 7. Paris, France: Didot Frères. p. 424.{{cite book}}: CS1 maint: multiple names: authors list (link) From p. 424: "10. Cystine. Cette substance a été découverte dans les calculs urinaires par Wollaston, […] je me suis donc permis de changer le nom qu'avait proposé cet homme distingué." (10. Cystine. This substance was discovered in urinary calculi by Wollaston, who gave it the name of "cystic oxide" because it dissolves as much in acids as in alkalis, and it resembles, in this respect, some metallic oxides; but, in a way, the reason [that was] alleged to justify it is not valid: I have therefore taken the liberty of changing the name that this distinguished man had proposed.)
  6. ↑ Thaulow, C. J. (1838). "Sur la composition de la cystine" [On the composition of cystine]. Journal de Pharmacie (in French). 24: 629–632.
  7. ↑ 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 .
  8. ↑ Mörner, K. A. H. (1899). "Cystin, ein Spaltungsprodukt der Hornsubstanz" [Cystine, a cleavage product of horn tissue]. Hoppe-Seyler's Zeitschrift für Physiologische Chemie (in German). 28 (5–6): 595–615. doi:10.1515/bchm2.1899.28.5-6.595.
  9. ↑ Erlenmeyer, Emil (1903). "Synthese des Cystins" [Synthesis of cystine]. Berichte der Deutschen Chemischen Gesellschaft (in German). 36 (3): 2720–2722. doi:10.1002/cber.19030360320.
  10. ↑ Erlenmeyer, E. jun.; Stoop, F. (1904). "Ueber die Synthese einiger α-Amido-β-hydroxysäuren. 2. Ueber die Synthese der Serins und Cystins" [On the synthesis of some α-amido-β-hydroxy acids. 2. On the synthesis of serine and cystine.]. Annalen der Chemie (in German). 337: 236–263. doi:10.1002/jlac.19043370205. Discussion of the synthesis of cystine begins on p. 241.
  11. ↑ Erlenmeyer's findings regarding the structure of cystine were confirmed in 1908 by Fischer and Raske. See: Fischer, Emil; Raske, Karl (1908). "Verwandlung des l-Serines in aktives natürliches Cystin" [Conversion of l-serine into [optically] active natural cystine]. Berichte der Deutschen Chemischen Gesellschaft (in German). 41: 893–897. doi:10.1002/cber.190804101169.
  12. ↑ Aslaksena, M.A.; Romarheima, O.H.; Storebakkena, T.; Skrede, A. (28 June 2006). "Evaluation of content and digestibility of disulfide bonds and free thiols in unextruded and extruded diets containing fish meal and soybean protein sources". Animal Feed Science and Technology. 128 (3–4): 320–330. doi:10.1016/j.anifeedsci.2005.11.008.
  13. ↑ Gahl, William A.; Thoene, Jess G.; Schneider, Jerry A. (2002). "Cystinosis". New England Journal of Medicine. 347 (2): 111–121. doi:10.1056/NEJMra020552. PMID   12110740.
  14. ↑ Frassetto L, Kohlstadt I (2011). "Treatment and prevention of kidney stones: an update". Am Fam Physician. 84 (11): 1234–42. PMID   22150656.
  15. ↑ "Cystine stones". UpToDate . Archived from the original on 26 February 2014. Retrieved 20 February 2014.
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