All Topics  
Cystine

 

 
   Email Print
   Bookmark   Link
 

 

Cystine
 
 
  Topics Cystine Topic Home

Cystine is the amino acid
Amino acid

In chemistry, an amino acid is a molecule containing both amine and carboxyl functional groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H2NCHRCOOH, where R is an organic substituent....
 dimer
Dimer

File:Carboxylic acid dimers.pngA dimer is a chemical or biological entity consisting of two identical subunits called monomers, which are held together by either intramolecular forces or weaker intermolecular forces....
 formed when a pair of cysteine
Cysteine

Cysteine is an a-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that humans can synthesize it....
 molecules are joined by a disulfide
Disulfide

In chemistry, a disulfide usually refers to the structural unit composed of a linked pair of sulfur atoms. The disulfide anion is S22-....
 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
William Hyde Wollaston

William Hyde Wollaston Royal Society was an English chemist and physicist who is famous for discovering two chemical elements and for developing a way to process platinum ore....
 but was not recognized as a component of proteins until it was isolated from the horn
Horn (anatomy)

A horn is a pointed projection of the skin on the head of various mammals, consisting of a covering of horn surrounding a core of living bone....
 of a cow in 1899. Through formation of disulfide bonds within and between protein molecules, cystine is a significant determinant of the tertiary structure
Tertiary structure

In biochemistry and chemistry, the tertiary structure of a protein or any other macromolecule is its three-dimensional structure, as defined by the atomic coordinates....
 of most proteins.






Discussion
Ask a question about 'Cystine'
Start a new discussion about 'Cystine'
Answer questions from other users
Full Discussion Forum



Encyclopedia


Cystine is the amino acid
Amino acid

In chemistry, an amino acid is a molecule containing both amine and carboxyl functional groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H2NCHRCOOH, where R is an organic substituent....
 dimer
Dimer

File:Carboxylic acid dimers.pngA dimer is a chemical or biological entity consisting of two identical subunits called monomers, which are held together by either intramolecular forces or weaker intermolecular forces....
 formed when a pair of cysteine
Cysteine

Cysteine is an a-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that humans can synthesize it....
 molecules are joined by a disulfide
Disulfide

In chemistry, a disulfide usually refers to the structural unit composed of a linked pair of sulfur atoms. The disulfide anion is S22-....
 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
William Hyde Wollaston

William Hyde Wollaston Royal Society was an English chemist and physicist who is famous for discovering two chemical elements and for developing a way to process platinum ore....
 but was not recognized as a component of proteins until it was isolated from the horn
Horn (anatomy)

A horn is a pointed projection of the skin on the head of various mammals, consisting of a covering of horn surrounding a core of living bone....
 of a cow in 1899. Through formation of disulfide bonds within and between protein molecules, cystine is a significant determinant of the tertiary structure
Tertiary structure

In biochemistry and chemistry, the tertiary structure of a protein or any other macromolecule is its three-dimensional structure, as defined by the atomic coordinates....
 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

The disulfide link is readily reduced to give the corresponding thiol, cysteine. This reaction is typically effected with thiols such as mercaptoethanol or dithiothreitol
Dithiothreitol

Dithiothreitol is the common name for a small-molecule redox reagent known as Cleland's reagent. DTT's formula is C4H10O2S2 and the molecular structure of its reduced form is shown at the right; its oxidized form is a disulfide bond 6-membered ring ....
. CO2H)2 + 2 RSH
Thiol

In organic chemistry, a thiol is a compound that contains the functional group composed of a sulfur atom and a hydrogen atom . Being the sulfur analogue of an alcohol group , this functional group is referred to either as a thiol group or a sulfhydryl group....
  ? 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
Denaturation (biochemistry)

Denaturation is a process in which proteins or nucleic acids lose their structure by application of some external stress or compound for example, treatment of proteins with strong acids or bases, high concentrations of inorganic salts, organic compound solvents , or heat....
 whey proteins from milk. The disulfide-bonded cystine is not digested or significantly hydrolized by the stomach, but is transported by the blood stream to the tissues of the body. Here, within the cells of the body, the weak disulfide bond is cleaved to give cysteine, from which glutathione
Glutathione

Glutathione is a tripeptide. It contains an unusual peptide linkage between the amino acid of cysteine and the carboxyl group of the glutamate side chain....
 can be synthesized.

In animal feed
Disulfide bonds can be broken at temperatures above about 150 °C
Celsius

Celsius is a temperature scale that is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death....
, especially at low moisture levels (below about 20%).

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.

See also

  • Cystinuria
    Cystinuria

    Cystinuria is an inherited autosome dominance metabolic disorder that is characterized by the formation of cystine stones in the kidneys, ureter, and Urinary bladder....
  • Cysteine
    Cysteine

    Cysteine is an a-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that humans can synthesize it....


External links