cystine

cys·tine

(sĭs'tēn') pronunciation

n.
A white crystalline amino acid, C₆H₁₂N₂O₄S₂, formed from the disulfide linkage of two cysteines during folding of many proteins, especially keratin, and stabilizing the tertiary structure of the protein.

[From its discovery in bladder stones.]

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cystine

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A molecule resulting from the oxidation reaction between the sulphydryl (–SH) groups of two cysteine molecules (see amino acid). This often occurs between adjacent cysteine residues in polypeptides. The resultant disulphide bridges (–S-S–) are important in stabilizing the structure of protein molecules.

Oxford Food & Nutrition Dictionary:

cystine

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The dimer of cysteine produced when its sulphydryl group (—SH) is oxidized forming a disulphide (—S—S—) bridge. Such disulphide bridges are especially important in maintaining the structure of proteins, and also in the rôle of the tripeptide glutathione as an antioxidant.

Oxford Dictionary of Biochemistry:

cystine

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the trivial name for dicysteine; β,β′-dithiodialanine; α,α′-diamino-β,β′-dithiobis(propionic acid); (R*,R′*)-3,3′-dithiobis(2-aminopropanoic acid);
HOOC−CH(NH₂)−CH₂−S−S−CH₂−CH(NH₂)−COOH;
a di(α-amino acid) with two chiral centres, formed by the oxidation of cystein. L-Cysteine,

(R,R′)-3,3′-dithiobis(2-aminopropanoic acid), is found in peptide linkage in proteins, having been formed by post-translational oxidation of cysteine. In mammals it is a nonessential dietary amino acid and is glucogenic. As it is somewhat insoluble in neutral aqueous solutions, it sometimes forms urinary stones. meso-Cystine, (R,S′)-3,3′-dithiobis(2-aminopropanoic acid), is the internally compensated achiral diastereoisomer, in which d- and l-half-molecules are combined. See also note at cysteine.

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Saunders Veterinary Dictionary:

cystine

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A naturally occurring amino acid, an important sulfur-containing component of the protein molecule. It is sometimes found in the urine and in the kidneys in the form of minute hexagonal crystals, frequently forming cystine calculus in the bladder.

Cystine stones. By permission from Nelson RW, Couto CG, Small Animal Internal Medicine, Mosby, 2003

c. calculi — see cystine uroliths.

Wikipedia on Answers.com:

Cystine

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Not to be confused with cysteine.

Cystine

Identifiers
CAS number	56-89-3^Y
ChemSpider	575^Y
UNII	48TCX9A1VT^Y
KEGG	C01420^Y
ChEBI	CHEBI:35492^Y
ChEMBL	CHEMBL366563^Y
Jmol-3D images	Image 1
SMILES C(C(C(=O)O)N)SSCC(C(=O)O)N
InChI 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)^Y Key: LEVWYRKDKASIDU-UHFFFAOYSA-N^Y 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
Properties
Molecular formula	C₆H₁₂N₂O₄S₂
Molar mass	240.3 g mol⁻¹
Hazards
MSDS	External MSDS
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Cystine is a dimeric amino acid formed by the oxidation of two cysteine residues that covalently link to make a disulfide bond. This organosulfur compound has the formula (SCH₂CH(NH₂)CO₂H)₂. It is a white solid, and melts at 247-249 °C. It was discovered in 1810 by William Hyde Wollaston but was not recognized as being derived of proteins until it was isolated from the horn of a cow in 1899.^[1] Through formation of disulfide bonds within and between protein molecules, cystine is a significant determinant of the tertiary structure of most proteins. Disulfide bonding, along with hydrogen bonding and hydrophobic interactions is partially responsible for the formation of the gluten matrix in bread. Human hair contains approximately 5% cystine by mass.^[2]

Properties and nutritional aspects

The disulfide link is readily reduced to give the corresponding thiol cysteine. This reaction is typically effected with thiols such as mercaptoethanol or dithiothreitol.

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

For this reason, the nutritional benefits and sources of cystine are identical to those for the more-common cysteine. Disulfide bonds cleave more rapidly at higher temperatures.^[3]

References

^ "cystine." Encyclopædia Britannica. 2007. Encyclopædia Britannica Online. 27 July 2007 www.britannica.com/eb/article-9028437/cystine
^ Gortner, R. A.; W. F. Hoffman, W. F. (1941), "l-Cystine", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV1P0194 ; Coll. Vol. 1: 194
^ M.A. Aslaksena, O.H. Romarheima, T. Storebakkena and A. Skrede (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.

E numbers

Colours (E100–199) • Preservatives (E200–299) • Antioxidants & acidity regulators (E300–399) • Thickeners, stabilisers & emulsifiers (E400–499) • pH regulators & anticaking agents (E500–599) • Flavour enhancers (E600–699) • Miscellaneous (E900–999) • Additional chemicals (E1100–1599)

Waxes (E900–909) • Synthetic glazes (E910–919) • Improving agents (E920–929) • Packaging gases (E930–949) • Sweeteners (E950–969) • Foaming agents (E990–999)

L-cysteine (E920) • L-cystine (E921) • Potassium persulfate (E922) • Ammonium persulfate (E923) • Potassium bromate (E924) • Chlorine (E925) • Chlorine dioxide (E926) • Azodicarbonamide (E927) • Carbamide (E927b) • Benzoyl peroxide (E928)

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		Oxford Food & Nutrition Dictionary. A Dictionary of Food and Nutrition. Copyright © 1995, 2003, 2005 by A. E. Bender and D. A. Bender. All rights reserved. Read more
		Oxford Dictionary of Biochemistry. Oxford University Press. Oxford Dictionary of Biochemistry and Molecular Biology © 1997, 2000, 2006 All rights reserved. Read more
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