|Jmol-3D images||Image 1|
|Molar mass||240.30 g mol−1|
| (what is: / ?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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. 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.
Properties and nutritional aspects 
- (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.
Cystine crystal morphology and presence in urine 
Cystine crystals are 6 sided and come in various sizes. They can be found in both human and mammal urine under a light microscope. The presence of cystine crystals is often indicative of amino acid reabsorption defects. Cystinuria has been reported to occur in many breeds of dogs. In humans the presence of cystine crystals is indicative of cystinosis, a rare genetic disease.
See also 
- Lanthionine, similar with mono-sulfide link
- "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.; 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.
- The Merck veterinary manual, Diagnostic Procedures for the Private Practice Laboratory. Captured online at merckvetmanual.com. March 2012.