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L-Cysteine Overview

L-cysteine is a protein amino acid naturally present in the proteins of life forms. L-cysteine is a sulfur amino acid and contains a sulfhydryl group. Although most cysteine is found in proteins, small amounts of free cysteine are found in body fluids and in plants. The normal diet contributes approximately 1 gram of L-cysteine daily.

L-cysteine is considered a nonessential amino acid, meaning that, under normal physiologic conditions, sufficient amounts of this amino acid are formed from the dietary essential amino acids L-methionine and the nonessential amino acid L-serine via a transsulfuration reaction. L-cysteine is a conditionally essential amino acid under certain circumstances, for example, for preterm infants.

L-cysteine serves as a very important precursor for synthesis of proteins, glutathione, taurine, coenzyme A, and inorganic sulfate. Glutathionine itself has a number of biochemical functions, including maintenance of normal cellular redox state. Certain conditions, e.g. an acetaminophen overdose, can deplete hepatic glutathione, and this can be life-threatening. The antidote to an acetaminophen overdose is L-cysteine, in the delivery form of N-acetylcysteine. The L-cysteine derived from N-acetylcysteine helps to restore hepatic glutathione. See N-acetylcysteine Overview.


Research Overview

Research on L-cysteine shows the following effects:
1. Prevents liver fibrosis
2. Has cytoprotective properties against toxicity
3. May modulate KYNA development in the brain
4. Prevents cataract formation
5. May help prevent ischemia-reperfusion injury in the lung
6. Cysteine deficiency leads to cellular dysfunction in HIV
7. Lowers blood, brain and liver alcohol levels caused by alcohol intoxication
8. Combats severe hypoglycemic attacks
9. May be a factor in cardiovascular control
10. May play a role in heavy metal detoxification

L-Cysteine Abstracts (31)