Cystein

Cystein is a semi-essential proteinogenic amino acid with the formula HO2CCH(NH2)CH2SH. It is encoded by the codons UGU and UGC. The thiol side chain in cysteine often participates in enzymatic reactions, as a nucleophile. The thiol is susceptible to oxidation to give the disulfide derivative cystine, which serves an important structural role in many proteins. When used as a food additive, it has the E number E920.

Structure and properties

Cysteine is named after cystine, its oxidized dimer. Both are derived from the Greek word kustis, meaning bladder, plus the ending -ine, a suffix used in the names of amino acids.

Cysteine is the chemical compound that is a semi-essential proteinogenic amino acid. It is encoded by the codons UGU and UGC in the genetic code. This means that it is a standard amino acid that can be used to make proteins after being attached to a transfer RNA molecule through the process of protein biosynthesis.

Biological functions

Cysteine is an important source of sulfur in human metabolism, and although it is classified as a non-essential amino acid, cysteine may be essential for infants, the elderly, and individuals with certain metabolic disease or who suffer from malabsorption syndromes. Cysteine can usually be synthesized by the human body under normal physiological conditions if a sufficient quantity of methionine is available.

Dietary sources

Cysteine is found in most high-protein foods, including:

• Animal sources: pork, sausage meat, chicken, turkey, duck, luncheon meat, eggs, milk, whey protein, ricotta, cottage cheese, yogurt.
• Plant sources: red peppers, garlic, onions, broccoli, brussels sprout, oats, granola, wheat germ, sprouted lentils.

See also

• Amino acid
• Protein biosynthesis
• Methionine
• Sulfur

Cystein Resources
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