CYSTINE is the oxidized dimer form of the amino acid cysteine and has the formula (SCH2CH(NH2)CO2H)2. It is a white solid that is slightly soluble in water. It serves two biological functions: a site of redox reactions and a mechanical linkage that allows proteins to retain their three-dimensional structure .
* 1 Formation and reactions
* 2 Biological transport
FORMATION AND REACTIONS
It 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. Human hair and skin contain approximately 10–14% cystine
by mass. It was discovered in 1810 by
William Hyde Wollaston
It is formed from the oxidation of two cysteine molecules, via the formation of a disulfide bond . In cell biology, cystine (found in proteins) can only exist in non-reductive (oxidative) organelles, such as the secretory pathway (ER, Golgi, Lysosomes, Vesicles and ECM). Meaning that in reductive conditions (Cytoplasm, Nucleus, etc.) cysteine is favorably found. 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.
The presence of cystine in urine is often indicative of amino acid reabsorption defects. Cystinuria has been reported to occur in dogs. In humans the excretion of high levels of cystine crystals can be indicative of cystinosis , a rare genetic disease.
CYSTINE HAIR NUTRITIONAL SUPPLEMENTS
Lanthionine , similar with mono-sulfide link
Protein tertiary structure
* ^ Nelson, D. L.; Cox, M. M.; Lehninger, Principles of Biochemistry. 3rd Ed. Worth Publishing: New York, 2000. ISBN 1-57259-153-6 . * ^ "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. CS1 maint: Multiple names: authors list (link ); Coll. Vol., 1, p. 194 * ^ M.A. Aslaksena; O.H. Romarheima; T. Storebakkena; 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 . * ^ Gahl, William A.; Thoene, Jess G.; Schneider, Jerry A. (2002). "Cystinosis". New England Journal of Medicine. 347 (2): 111–121. ISSN 0028-4793 . PMID 12110740 . doi :10.1056/NEJMra020552 .
* v * t * e
* Colours (E100–199) * Preservatives (E200–299) * Antioxidants & acidity regulators (E300–399) * Thickeners , stabilisers & emulsifiers (E400–499) * pH regulators