Metabolism / Metabolites
L-cysteine is a core compound in human sulfur metabolism. In proteins, the formation of disulfide bonds between cysteine sulfhydryl groups plays a crucial role in protein tertiary structure and enzyme activity; however, cysteine is always incorporated into polypeptide chains in its cysteine form. L-cysteine is degraded to pyruvate in two steps: desulfurization and transamination. Cysteine can be metabolized to taurine and carbon dioxide via the cysteine sulfinate pathway, the first step of which is the oxidation of cysteine to cysteine sulfinate. This step is catalyzed by cysteine dioxygenase. Cysteine sulfinate can be decarboxylated to taurine, or metabolized to pyruvate and sulfite via the putative intermediate β-sulfinylpyruvate, ultimately producing carbon dioxide and sulfate. Amino acid catabolism is essential for regulating the size of the free amino acid pool and participates in energy production and nutrient reuse. The carbon skeleton is typically converted into precursors or intermediates of the tricarboxylic acid cycle. For cysteine, the reduced sulfur derived from the thiol group must also be oxidized to prevent its accumulation to toxic concentrations. This article introduces a mitochondrial sulfur catabolism pathway that catalyzes the complete oxidation of L-cysteine to pyruvate and thiosulfate. After L-cysteine is transaminated to 3-mercaptopyruvate, its thiol group is transferred to glutathione via thiotransferase 1 and oxidized to sulfite by the sulfur dioxygenase ETHE1. Subsequently, thiotransferase 1 adds a second persulfate group, converting the sulfite to thiosulfate. This pathway is most important in early embryonic development and vegetative growth under light-limited conditions. Characterization of double mutants generated from Arabidopsis thaliana ETHE1 and thiotransferase 1 T-DNA insert lines revealed that intermediates in the ETHE1-dependent pathway (likely persulfates) interfere with amino acid catabolism and induce early senescence. Uremic toxins often accumulate in the blood due to overeating or poor renal filtration. Most uremic toxins are metabolic waste products, usually excreted in urine or feces.

Toxicity Summary
It is safe at the current methods of use and concentrations. Ingredients, concentrations, and usage information can be found at: https://cir-reports.cir-safety.org
Identification and Uses: Cysteine forms white or colorless crystals. It is used in biochemical and nutritional research and is also used as a reducing agent in bread dough (maximum concentration 90 ppm). It is also used as a flavoring agent and in pharmaceuticals, including veterinary drugs. Human Exposure and Toxicity: A 3% cysteine solution is non-irritating to the human eye. Animal Studies: A single instillation of 0.1 g of L-cysteine into the eye of a rabbit produced a mild irritant effect, which was completely reversible within 48 hours. A single application of 0.5 g of L-cysteine to the skin of three rabbits showed no irritation or corrosive effects. Rats treated with high doses of cysteine experienced reduced litter size, which was associated with degeneration and/or death of ovulated unfertilized eggs and embryos, accompanied by changes in the zona pellucida, which was affected in the ovary. Subcutaneous injection of 1.2 mg/g cysteine into pregnant mice and rats on the last day of pregnancy resulted in brain degeneration in the fetuses one day later. Using the Chinese hamster V79 cell line, L-cysteine was considered non-mutagenic at the HPRT locus. L-cysteine did not induce chromosomal structural aberrations in the V79 Chinese hamster cell line. Ecotoxicity studies: This study aimed to determine the effects of cysteine on sperm motility, duration of sperm motility, DNA damage, and fertility in carp (Cyprinus carpio) after thawing. Cysteine supplementation improved fertilization and hatching rates and reduced DNA damage. Uremic toxins (such as cysteine) can be actively transported to the kidneys via organic ion transporters (especially OAT3). Elevated uremic toxin levels can stimulate the production of reactive oxygen species. This appears to be mediated by the direct binding of uremic toxins to or inhibition of NADPH oxidases (especially NOX4, which is abundant in the kidneys and heart) (A7868). Reactive oxygen species (ROS) can induce various DNA methyltransferases (DNMTs) that participate in the silencing of the KLOTHO protein. KLOTHO has been shown to play an important role in anti-aging, mineral metabolism, and vitamin D metabolism. Multiple studies have shown that in acute or chronic kidney disease, KLOTHO mRNA and protein levels are reduced due to elevated local ROS levels (A7869). Although cysteine is classified as a non-essential amino acid, it can be crucial for infants, the elderly, and individuals with certain metabolic disorders or malabsorption syndromes. Under normal physiological conditions, the human body can usually synthesize cysteine if methionine is sufficient. Cysteine possesses antioxidant properties due to the redox reactions of thiols. The antioxidant properties of cysteine are often manifested in the tripeptide glutathione, which is present in the human body and other organisms. The systemic bioavailability of orally administered glutathione (GSH) is extremely low; therefore, it must be biosynthesized from its constituent amino acids—cysteine, glycine, and glutamate. Glutamic acid and glycine are readily available in the diets of most industrialized countries, but cysteine supply may be a limiting substrate. Cysteine is also an important source of sulfides in human metabolism. Sulfides in iron-sulfur clusters and nitrogenase are extracted from cysteine, which is converted to alanine in the process. In a 1994 report jointly released by the five major tobacco companies, cysteine was listed as one of 599 cigarette additives. However, like most cigarette additives, its use or purpose is not yet clear. Adding cysteine to cigarettes may have two benefits: first, as an expectorant, since smoking increases the production of mucus in the lungs; and second, to increase the beneficial antioxidant glutathione (smokers have lower levels of glutathione in their bodies).

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Non-Human Toxicity Values
Rat dermal LD50 >2000 mg/kg body weight
Rats oral LD50 1890 mg/kg
Rats intraperitoneal LD50 1620 mg/kg
Rats dermal LD50 1550 mg/kg
For more non-human toxicity data (complete) for cysteine (7 types), please visit the HSDB record page.

L-cysteine is an optically active cysteine with an L-configuration. It is used as a flour treatment agent, a human metabolite, and an inhibitor of EC 4.3.1.3 (histidine ammonia-lyase). It is a serine family amino acid, a protein-synthesizing amino acid, cysteine, and an L-α-amino acid. It is the conjugate base of L-cysteine. It is the conjugate acid of L-cysteine (1-). It is the enantiomer of D-cysteine. It is the zwitterion tautomer of L-cysteine. Cysteine is a thiol-containing non-essential amino acid that can be oxidized to cystine. L-cysteine is a metabolite found or produced in Escherichia coli (K12 strain, MG1655 strain). Cysteine has also been reported in Indigofera tinctoria, pomegranate, and other organisms with relevant data. Cysteine is an essential sulfur-containing amino acid for humans and is associated with cystine. Cysteine is crucial for protein synthesis, detoxification, and various metabolic functions. Cysteine is found in β-keratin, a major protein in nails, skin, and hair. Cysteine is crucial for collagen production and the elasticity and texture of the skin. It is also an essential amino acid for the synthesis of taurine, a component of the antioxidant glutathione, and plays a role in the metabolism of important biochemicals such as coenzyme A, heparin, and biotin. (NCI04)
Cysteine is a uremic toxin. Based on their chemical and physical properties, uremic toxins can be classified into three main categories: 1) small molecule, water-soluble, non-protein-bound compounds, such as urea; 2) small molecule, lipid-soluble, and/or protein-bound compounds, such as phenols; 3) larger so-called medium molecules, such as β2-microglobulin. Long-term exposure to uremic toxins can lead to various diseases, including kidney damage, chronic kidney disease, and cardiovascular disease.
Cysteine is a naturally occurring sulfur-containing amino acid found in most proteins, but in small amounts. Among the 20 naturally occurring amino acids, cysteine is unique in that it contains a sulfhydryl group. The thiol group can undergo redox reactions; cysteine, when oxidized, can form cystine, which is composed of two cysteine residues linked by a disulfide bond. This reaction is reversible: reducing the disulfide bond regenerates two cysteine molecules. The disulfide bond of cystine is crucial for the structure of many proteins. Cysteine commonly participates in electron transfer reactions and helps enzymes catalyze reactions. Cysteine is also a component of the antioxidant glutathione. N-acetyl-L-cysteine (NAC) is a form of cysteine in which the acetyl group is attached to the nitrogen atom of cysteine and is sold as a dietary supplement. The name cysteine comes from the Greek word kustis, meaning bladder—cysteine was originally isolated from kidney stones. Because cysteine contains a thiol group, it can undergo redox reactions. Oxidation of cysteine can form disulfide bonds with other thiols or be further oxidized to produce sulfinic acids or sulfonic acids. The thiol group of cysteine is also nucleophilic and can undergo addition and substitution reactions. Thiol groups exhibit significantly enhanced reactivity upon ionization. Cysteine residues in proteins have near-neutral pKa values, thus they typically exist intracellularly as reactive thiolates. Thiol groups have a high affinity for heavy metals, allowing cysteine-containing proteins to bind tightly to metals such as mercury, lead, and cadmium. Cysteine possesses antioxidant properties due to its redox capabilities. Cysteine is an important source of sulfur in human metabolism. Although classified as a non-essential amino acid, it may be essential for infants, the elderly, and individuals with certain metabolic disorders or malabsorption syndromes. In the future, cysteine may be recognized as an essential or conditionally essential amino acid. Cysteine plays a crucial role in energy metabolism. It exists in the form of cystine and is a structural component of many tissues and hormones. Cysteine has a wide range of clinical applications, from treating hair loss and psoriasis to preventing smoking-induced coughs. In some cases, oral cysteine therapy has proven highly effective in treating asthma and can help patients discontinue theophylline and other medications. In addition, cysteine can enhance the effectiveness of topical silver, tin, and zinc salts in preventing tooth decay. In the future, cysteine may play a role in treating cobalt poisoning, diabetes, mental illness, cancer, and epilepsy. Cysteine is a thiol-containing non-essential amino acid that oxidizes to form cystine. See also: Cysteine hydrochloride (salt form)... See more...

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Drug Indications
For the prevention of liver and kidney damage caused by acetaminophen overdose

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Mechanism of Action
Under normal physiological conditions, the human body can usually synthesize cysteine if methionine is sufficient. Cysteine is usually synthesized in the body when methionine is sufficient. Cysteine has antioxidant properties and participates in redox reactions. The antioxidant properties of cysteine are usually manifested in the tripeptide glutathione, which is present in the human body and other organisms. Due to the limited bioavailability of glutathione (GSH) in the body, it usually needs to be biosynthesized from its constituent amino acids—cysteine, glycine, and glutamate. Glutamic acid and glycine are abundant in the diets of most industrialized countries, but cysteine supply may be a limiting substrate. In human metabolism, cysteine participates as a precursor in the formation of iron-sulfur clusters and sulfides in nitrogenase. In a 1994 report by five top cigarette companies, cysteine was listed as one of 599 additives in cigarettes. However, like most cigarette additives, its use or purpose remains unclear. Adding cysteine to cigarettes may offer two benefits: firstly, as an expectorant, since smoking increases the production of mucus in the lungs; and secondly, by increasing the beneficial antioxidant glutathione (which is lower in smokers).

C3H7NO2S

121.15

121.019

52-90-4

62488-11-3;7048-04-6 (Hydrochloride)

5862

Colorless crystals
White crystals

1.3±0.1 g/cm3

293.9±35.0 °C at 760 mmHg

260 °C decomposes ; 220 °C

131.5±25.9 °C

0.0±1.3 mmHg at 25°C

1.550

0.23

3

4

2

7

75.3

1

S([H])C([H])([H])[C@@]([H])(C(=O)O[H])N([H])[H]

XUJNEKJLAYXESH-REOHCLBHSA-N

InChI=1S/C3H7NO2S/c4-2(1-7)3(5)6/h2,7H,1,4H2,(H,5,6)/t2-/m0/s1

(2R)-2-amino-3-sulfanylpropanoic acid

Cysteinum; FEMA No. 3263; Cysteine

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

May dissolve in DMSO (in most cases), if not, try other solvents such as H2O, Ethanol, or DMF with a minute amount of products to avoid loss of samples

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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 (Please use freshly prepared in vivo formulations for optimal results.)