Cystine

• (R, R)- cysteine
• L-( -)- cystine
• IUPAC: (2R, 2'R ) -3,3 '- dithiobis ( 2-amino- propanoic acid )

V06DD

White powder with faint characteristic odor

Amino acid

Fixed

260-261 ° C ( decomposition)

1

Very poor in water ( 190 mg · l-1 at 20 ° C)

25000 mg · kg -1 ( LD50, rat, oral)

Template: Infobox chemical / molecular formula search available

L-cystine [ Synonym: (R, R)- cysteine ​​] is a disulfide formed by oxidation of two molecules of the amino acid L -cysteine ​​[ Synonym: (R) -cysteine ​​] is produced.

Discovery and natural occurrence

The natural proteinogenic α - amino acid L- cystine was discovered in 1810 by William Hyde Wollaston and is found in high concentration in peptide bound in the cells of the immune system, the skin and the hair.

So Keratin contains ( from hair, bristles or feathers ) about 11 % peptide- bound L- cystine. There is also kidney stones, consisting of L- cystine.

Production and recovery

The majority of the currently used in the food industry, L- cystine is obtained by fermentation. These genetically modified bacteria type Escherichia coli are used. The formed by the microorganisms L- cystine can be then purified and crystallized. Since only the bacterial strains, but their growing medium were not modified genetically modified DNA and no longer remains in the product, the obtained L- cystine is not classified as genetically modified.

A second manufacturing process is the acid hydrolysis of keratin proteins, such as poultry feathers, hair and hooves. This is obtained after neutralization a protein that consists of the 20 proteinogenic α -amino acids. From this, an L- cystine and L-tyrosine - rich fraction win easily by separating the highly water-soluble amino acids as L- cystine and L-tyrosine dissolve only slightly in water. To date, L- cystine is obtained commercially by this simple separation method.

Isomerism

The enantiomer of the natural L- cystine, D -cystine [ Synonyms: (S, S)- cystine ]. It has as well as the third stereoisomer is the meso - cystine, no practical significance.

Use

The electrochemical reduction of L- cystine ( disulfide a ) provides the L- cysteine ​​( thiol ). From L- cystine many drugs are manufactured on an industrial scale, for example, ( R )-S- carboxymethylcysteine ​​and (R )-N- acetylcysteine.

Cystine can be (as well as cysteine, E920 ) used in flour - treatment. Both amino acids alter the properties of the adhesive in wheat flour dough. While cystine strengthens the gluten structure, the dough does so less ductile, cysteine ​​loosens the gluten structure and makes the dough stretchy thereby.

Trade names

Pantogar (A), Pantovigar (D), prioress (A, D)