Cysteine is classified as a nonessential amino acid, but cysteine may be essential for infants, the elderly, and individuals with certain metabolic diseases or malabsorption syndromes. Cysteine is an important structural and functional component of many proteins and enzymes. Cysteine is named after cystine, its oxidized dimer. Cysteine is potentially toxic and is catabolized in the gastrointestinal tract and blood. Conversely, cysteine is absorbed during digestion as cystine, which is more stable in the gastrointestinal tract. Cystine travels to cells and is reduced to two cysteine molecules upon cell entry.
The measurement of cysteine, along with 23 other amino acids, is included in the Amino Acids in Plasma and the Amino Acids in Urine tests.
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Cysteine (Cys/C) is a sulfur-containing amino acid that is unstable in the air. In proteins, it usually exists as a cystine by forming a disulfide bond between two cysteine residues, carefully protected inside the protein to function as a stabilizer for the high-order structure of the protein or an active center for its bioactivity.
Cysteine is a powerful antioxidant that can potentially trap reactive oxygen species (ROS) and is promising as an antiaging active. Because cysteine tends to be absorbed into cells where it cannot exhibit its antioxidant properties, N-acetyl cysteine (NAC) is often used instead. In addition, cysteine has skin-whitening properties. During the biosynthesis process of melanin, cysteine accelerates the pathway directed to the formation of pheomelanin, which produces yellowish or reddish colors and blocks the formation of eumelanin, making dark colors.
Cysteine is an amino acid necessary for making protein and other metabolic functions. It is found in beta-keratin, the protein in nails, skin, and hair. Cysteine is also vital in creating collagen, which affects skin elasticity and texture.
L-cysteine is a non-essential amino acid that can be synthesized in the body from L-methionine and L-serine. It is conditionally essential for preterm infants. It is a necessary precursor for synthesizing proteins such as glutathione, taurine, coenzyme A, and inorganic sulfate. Some anti-inflammatory properties have been shown by L-cysteine and are essential for protecting against various toxins.
Cysteine can be endogenously synthesized mainly in the liver, from homocysteine issued from the transmethylation of methionine. Our body's cysteine is created from methionine, an essential amino acid. Some cysteine foods are pork, duck, turkey, chicken, yogurt, cheese, oat flakes, wheat germ, lunch meat, beef liver, etc.
Cysteine is used as a constituent in the food, pharmaceutical, and personal care industries.
