Cystine

Structural formula
Structural formula of (natural) L - (-) - cystine
General
Surname	Cystine
other names	( R , R ) -cystine L - (-) - cystine IUPAC : (2 R , 2 ′ R ) -3,3′-dithiobis (2-aminopropanoic acid)
Molecular formula	C 6 H 12 N 2 O 4 S 2
Brief description	white powder with a faint odor
External identifiers / databases
CAS number 56-89-3 ( L- cystine) EC number 200-296-3 ECHA InfoCard 100,000,270 PubChem 67678 ChemSpider 60997 DrugBank DB00138 Wikidata Q408626
Drug information
ATC code	V06 DD
Drug class	amino acid
properties
Molar mass	240.30 g mol −1
Physical state	firmly
Melting point	260–261 ° C (decomposition)
pK s value	1
solubility	very bad in water (190 mg l −1 at 20 ° C)
safety instructions
Please note the exemption from the labeling requirement for drugs, medical devices, cosmetics, food and animal feed GHS labeling of hazardous substances no GHS pictograms H and P phrases H: no H-phrases P: no P-phrases
Toxicological data	25000 mg kg −1 ( LD 50 ,  rat ,  oral )
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Cystine is a chemical compound . It is a disulfide that is formed from two molecules of the proteinogenic α- amino acid cysteine through oxidation of their sulfhydryl groups (–SH).

L - Cystine[Synonym: (R,R) -Cystine] is the naturally occurringenantiomer. CommonlyL-cystine is meant when the termcystine is usedwithout adescriptor.

Discovery and natural occurrence

The naturally occurring cystine was discovered in 1810 by William Hyde Wollaston as "cystic oxide" in bladder stones , and the monomeric cysteine only 74 years later . The sulfur-containing amino acid is also found in high concentrations in a peptide bond in the cells of the immune system , the skin and especially the hair .

Hair is made up of keratin, the proteins of which contain up to 17% L - cysteine , which can form disulfide bridges . (Painting by Sophie Gengembre Anderson (1823–1903): Girl with Long Hair)

Keratins , the fibrous proteins of the horny substance , of hair, bristles or feathers, contain around 11% L- cystine. It arises from the formation of disulfide bridges between L- cysteine ​​side chains in different protein sections. The more your fiber components are cross-linked, the stiffer the keratin fibers become. The bound cystine is formed here from the cysteine ​​building blocks bound in the polypeptide, not through the incorporation of free cystine.

There are also kidney stones that consist of L- cystine.

Isomerism

Cystine is chiral because it contains two stereocenters. Only one enantiomer, L- cystine [synonym: ( R , R ) -cystine], occurs naturally. Its mirror image, D- cystine [synonym: ( S , S ) -cystine], like the third stereoisomer, the meso- cystine, has no practical significance.

Isomers of cystine
Surname	L- cystine	D- cystine	meso- cystine
other names	( R , R ) -cystine (-) - cystine	( S , S ) -cystine (+) - cystine	( R , S ) -cystine ( S , R ) -cystine
Structural formula
CAS number	56-89-3	349-46-2	6020-39-9
	923-32-0 (DL)
EC number	200-296-3	206-486-2
	213-094-5 (DL)
ECHA info card	100,000,270	100,005,897
	100.011.904 (DL)
PubChem	67678	6857538	6991966
	595 (DL)
Wikidata	Q408626	Q27116494	Q27282385
	Q27102343 (DL)

Manufacture and extraction

Today , L- cystine is mostly produced by fermentation for use in the food industry. Genetically modified bacteria of the Escherichia coli type are used here. The L- cystine formed by the microorganisms can then be purified and crystallized. Since only the bacterial strains, but not their nutrient substrate, have been genetically modified and no more modified DNA remains in the product, the L- cystine obtained is not classified as genetically modified.

A second manufacturing process is the acid hydrolysis of keratin-containing proteins such as poultry feathers, hair and hooves. Here, after neutralization, a protein hydrolyzate is obtained that consists of about 20 proteinogenic α-amino acids. A fraction rich in L- cystine and L - tyrosine can easily be obtained from this by separating off the readily water-soluble amino acids, since L- cystine and L- tyrosine are only slightly soluble in water. To date, L- cystine is obtained commercially using this simple separation method.

use

The electrochemical reduction of L- cystine (a disulfide ) yields L- cysteine ​​(a thiol ). Numerous drugs are manufactured from L- cystine on an industrial scale, e.g. B. ( R ) - S - carboxymethylcysteine and ( R ) - N - acetylcysteine .

Cystine (like cysteine, E920 ) can be used in flour treatment. Both amino acids change the properties of the gluten in wheat flour dough. While cystine strengthens the glue structure, making the dough less elastic, cysteine ​​loosens the glue structure and makes the dough more elastic.

Trade names

Combination preparations

Pantogar (A), Pantovigar (D), Prioress (A, D)

Individual evidence

1. ↑ ^{a b c} data sheet (R) - (-) - cystine (PDF) from Merck , accessed on December 6, 2018.
2. ↑ ^{a b c d} Entry on cystine in the ChemIDplus database of the United States National Library of Medicine (NLM), accessed on August 9, 2016.
3. ↑ Hans-Dieter Jakubke and Hans Jeschkeit: Amino acids, peptides, proteins , Verlag Chemie, Weinheim, 1982, ISBN 3-527-25892-2 .
4. ↑ Yoshiharu Izumi, Ichiro Chibata and Tamio Itoh: Production and Use of Amino Acids , Angewandte Chemie 90 (1978) 187-194.