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cystine

 
Dictionary: 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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Chemistry Dictionary: 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.



 
Food and Nutrition: 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.

 

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: Cystine
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Cystine
Identifiers
CAS number [56-89-3]
Properties
Molecular formula C6H12N2O4S2
Molar mass 240.3 g mol−1
Hazards
MSDS External MSDS
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox references

Cystine is the amino acid dimer formed when a pair of cysteine molecules are joined by a disulfide bond. It is described by the formula (SCH2CH(NH2)CO2H)2. It is a colorless solid, and melts at 247-249 °C. It was discovered in 1810 by William Hyde Wollaston but was not recognized as a component 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]

Contents

Properties

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

Nutritional sources

Supplemental N-acetyl cysteine is claimed to be a source of cystine, but the dose of this supplement is limited by side effects. One of the richest nutritional sources of cystine in the diet is undenatured whey proteins from milk.[citation needed] The disulfide-bonded cystine is not digested or significantly hydrolyzed by the stomach, but is transported by the blood stream to the tissues of the body.[citation needed] Here, within the cells of the body, the weak disulfide bond is cleaved to give cysteine, from which glutathione can be synthesized.[citation needed]

In animal feed

Disulfide bonds can be broken at temperatures above about 150 °C, especially at low moisture levels (below about 20%)[3].

Side effects

Nutritional sources of cystine are virtually free of the toxic side effects associated with the single molecule of cysteine, N-acetyl cysteine. The greatest dietary source of cystine is bio-active, unpasteurized or low-heat pasteurized undenatured whey proteins.[citation needed]

See also

References

  1. ^ "cystine." Encyclopædia Britannica. 2007. Encyclopædia Britannica Online. 27 July 2007 www.britannica.com/eb/article-9028437/cystine
  2. ^ Gortner, R. A.; W. F. Hoffman, W. F. (1941). "l-Cystine". Org. Synth.; Coll. Vol. 1: 194. 
  3. ^ 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. 



 
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Copyrights:

Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved.  Read more
Chemistry Dictionary. A Dictionary of Chemistry. Sixth Edition. Copyright © Market House Books Ltd, 2008. All rights reserved.  Read more
Food and Nutrition. A Dictionary of Food and Nutrition. Copyright © 1995, 2003, 2005 by A. E. Bender and D. A. Bender. All rights reserved.  Read more
Veterinary Dictionary. Saunders Comprehensive Veterinary Dictionary 3rd Edition. Copyright © 2007 by D.C. Blood, V.P. Studdert and C.C. Gay, Elsevier. All rights reserved.  Read more
Wikipedia. This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Cystine" Read more