L-cysteine

L-cysteine is a semi-essential amino acid that is synthesized in the human body. It is classified as a proteinogenic amino acid, meaning it is used in the biosynthesis of proteins. L-cysteine is unique among the 20 standard amino acids due to its ability to form disulfide bridges, which contribute to the folding and stability of some proteins.

Structure and properties

L-cysteine has a chemical formula of C3H7NO2S. It is a chiral molecule, and its stereoisomer is D-cysteine. The L-isomer is the one that is involved in protein synthesis. The side chain of L-cysteine contains a thiol group, which is responsible for its reactivity and its ability to form disulfide bonds.

Biosynthesis

In humans, L-cysteine is synthesized from the amino acid serine through a series of enzymatic reactions. The process also requires the presence of methionine, another amino acid. This synthesis process is regulated by the body's needs, making L-cysteine a semi-essential amino acid.

Functions

L-cysteine plays several important roles in the body. It is a component of the antioxidant glutathione, which protects cells from damage by reactive oxygen species. L-cysteine is also involved in the synthesis of coenzyme A, a molecule that is essential for many metabolic processes. In addition, L-cysteine contributes to the structure of proteins by forming disulfide bonds.

Dietary sources and supplements

L-cysteine is found in most high-protein foods, including meat, dairy products, eggs, and some grains and vegetables. It can also be taken as a dietary supplement, often in the form of N-acetyl-L-cysteine (NAC), which is more stable and better absorbed by the body.

Health implications

L-cysteine has been studied for its potential health benefits, including its antioxidant properties and its role in detoxification processes. Some research suggests that L-cysteine supplements may help to improve immune function, respiratory health, and neurological health, although more studies are needed to confirm these effects.

See also

• Amino acid
• Protein
• Disulfide bond
• Glutathione
• Coenzyme A

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