What is Cysteine?

People take different foods in order to live healthy. The role that proteins play in our body cannot be underestimated. We need proteins for growth, repair and replacement of worn out tissues and muscles. We cannot talk of proteins without mentioning amino acids because they form the basis of proteins. Similarly, there is this type of amino acid called Cysteine, whose amazing facts will surprise you. What does it do? It is worth looking at. See why.

Definition of Cysteine


Cysteine is a protein component which is a non essential amino acid that plays a huge role in protein synthesis, detoxification and various metabolic reactions in the body. Its molecular formula is HO2CCH(NH2)CH2CH>. It is normally shortened as Cys or simply as C. Cysteine is encoded by UCU and UGC codons. Cysteine contributes towards enzymatic reactions in the human body. It plays this very important role in the form of a nucleophile. When thiol is oxidized, it results into disulfide from which we obtain cysteine.

Cysteine synthesis


Cysteine can naturally be manufuctured by the body under normal physiological conditions with availability of methionine in adequate amounts.

Sources of Cysteine

  • We can get cysteine from different plants such as garlic, onion, broccoli, oats, brussels sprout, red pepper e.t.c
  • Animal sources of cysteine include meat, dairy products as well as eggs.
  • Hydrolysis of human hair, hog hair and chicken feathers in industries
  • Synthetic manufacture through fermenting a mutant of E.Coli which leads to the production of L-cysteine.

Importance of cysteine in the body


1.Precursor to glutathione.
Glutathione, abbreviated as GSH is a very significant antioxidant which helps to prevent damage to the components of cells. Such damage could be brought about by reactive oxygen species such as free radicals, peroxides e.t.c. Glutathione is made from cysteine and it is the form through which cystein expresses it antioxidant properties.
2.Attaching of cations.
Cystein helps to bind metal ions(cations). Its residues help to bind enzyme co-factors to thiolate substituent. For example Iron (Fe) in Cytochrome P450. In addition, the thiol group has high affinity for heavy metals.Therefore proteins containing cysteine will bind metals like mercury and led.
3.Source of sulphur 
Cysteine helps to provide sulfide, a sulphur component which is important in body metabolism. The sulphur that is found in nitrogenase and iron sulphur clusters is gotten from cysteine.

Classification of Cysteine


Cysteine FoodsInitially, it was classified as a hydropholic amino acid. This is because of its chemical that is parallel between its thiol and hydroxyl group in other polar amino acids’ side chain. Cysteine's side chain has however shown to stabilize hydrophobic interactions in milcelles to a greater degree than the side chain in the non-polar polar amino acid group like glycine and the polar amino acid like serine. In an analysis involving statistics of the number of times with which amino acids appear in different chemical environments in protein structure, free cysteine residues were found to associate with hydrophobic regions of proteins.

Their hydrophobic tendency was equivalent to that of non polar amino acids such as methionine and tyrosine. Morever, it was more than that of commonly known polar amino acids such as serine and threonine. Hydrophobicity scales is used for ranking amino acids from less hydrophobic to hydrophobic. This scale usually places cysteine towards the hyrophobic end of the spectrum even when they are based on methods that are not subject to influence if cysteine is to form disulphide bonds in protein. For this reason, cysteine is mainly classified under hydrophobic amino acids even though it may slightly be categorized as polar and non polar.

Cysteine in formation of protein structure


In proteins, cysteine residues can occur freely or be bonded. Through covalent bonding , they are able to attach themselves to other cysteine residues and form disulphide bonds. This bond helps in folding and stabilizing proteins. Disulphide bonds which help in folding proteins are formed from oxidation of thiol group which is a protein residue. Oxidants that are more aggressive convert cysteine to sulfinic and sulphonic acid. Cysteine residues then crosslinks the proteins thus enhancing their firmness.
In the interior of the cell, disulphide bridges between cysteine residue within a polypeptide support. Insulin is a good example of a crosslinked protein. Two of its separate peptide chains are linked by a pair of disulphide bonds.

Uses of Cysteine

It is commonly used in the manufacture of food flavors. For instance, when cysteine reacts with sugar in Mailland reaction, the result is some meat flavor. In terms of personal care, cysteine is used for making a permanent wave. It is also used to break the disulfide bonds contained in keratin.

Cysteine is also used as a preventive measure for alcohol. It helps to counter the negative effects of alcohol on the human body which include liver damage that subsequently leads to cirrhosis. It also helps to lessen cases like hangover's among alcoholics. Cysteine achieves this by counteracting the negative effects of acetaldehyde. It facilitates the next metabolism process that converts the harmful acetaldehyde into harmless acetic acid that will not have a negative impact on the health of an alcoholic person.
It is widely used in experiments in order to investigate molecular structure and dynamics. For instance Maleimides will selectively attach to cysteine using Covalent Michael addition. Cysteine is also used in other experiments such as EPR’s site-directed spin labeling and paramagnetic enhanced NMR.


It is also used as an additive to cigarettes. It serves to act as an expectorant and also helps to provide glutathione oxidant that is usually deficient in a smoker’s body.

Making of supplements

Cysteine is immensely used in making of supplements. A common example is N-Acetyl cysteine. It is used as a supplement in the diet as well, as an antidote in case one takes an overdose of acetaminophene. In animals such as sheep, cysteine becomes very important too. This is because it helps the sheep in producing wool e.g merino type that is reared for wool production purposes. Cysteine is therefore a very elemental amino acid that they need to take. Today, some sheep have been n developed with the exceptional ability to produce their own cysteine. Such include transgenic sheep.

Cysteine is indeed a very important amino acid not only in our bodies but also in various applications in life. People should be encouraged to take a diet rich in cysteine in order to increase the level of this semi-essential amino acid in the body. It has immense health benefits. Cysteine will certainly contribute positively towards good health. It is such an important protein component.