L-CYSTEINE

L-Cysteine contains a reactive thiol (-SH) group, which gives it important chemical and biological properties.
L-Cysteine improves protein structure formation and antioxidant activity.
L-Cysteine is an optically active (L-form) amino acid that participates in protein synthesis and forms disulfide bonds (–S–S–) with other cysteine molecules.

CAS Number: 52-90-4
Molecular Formula: C3H7NO2S
Molecular Weight: 121.16
EINECS Number: 200-158-2

Synonyms: L-cysteine, cysteine, Cystein, Thioserine, Half-cystine, (R)-2-Amino-3-mercaptopropanoic acid, L-(+)-Cysteine, beta-Mercaptoalanine, L-Cystein, Cysteinum, (2R)-2-amino-3-sulfanylpropanoic acid, L-Cys, cisteina, Half cystine, 2-Amino-3-mercaptopropionic acid, L-Alanine, 3-mercapto-, FREE CYSTEINE, Cisteinum, FEMA No. 3263, Cisteinum [Latin], NSC-8746, alpha-Amino-beta-thiolpropionic acid, L-2-Amino-3-mercaptopropionic acid, beta-Mercaptoalanine, L-, (2R)-2-amino-3-mercaptopropanoic acid, L Cysteine, alpha-Amino-beta-thiolpropionic acid, L-, AI3-26559, alpha-Amino-beta-mercaptopropanoic acid, L-, Propanoic acid, 2-amino-3-mercapto-, (R)-, CHEBI:17561, 2-Amino-3-mercaptopropanoic acid, (R)-, E 920, K848JZ4886, 2-amino-3-mercaptopropanoate, E920, DTXSID8022876, CHEBI:15356, Cisteinum (Latin), (2R)-2-amino-3-mercaptopropanoate, (2R)-2-amino-3-sulfanylpropanoate, E921, l-cysteinum, l-cystAine, L-Cysteine High, 2-azaniumyl-3-sulfanylpropanoate, L-Cysteine 7403, RefChem:6415, L-Cysteine High 7404, DTXCID302876, (R)-2-Amino-3-sulfanyl-propanoic acid, (2R)-2-amino-3-mercapto-propionic acid;hydrochloride, 200-158-2, (2R)-2-azaniumyl-3-sulfanylpropanoate, 2-Amino-3-mercaptopropanoic acid, 2-amino-3-sulfanylpropanoic acid, (R)-Cysteine, Cysteine, L-, H-Cys-OH, (R)-2-Amino-3-mercaptopropionic acid, Cysteine [INN], Cisteina [Spanish], L-2-Amino-3-mercaptopropanoic acid, Cysteinum [INN-Latin], Cisteina [INN-Spanish], CCRIS 912, HSDB 2109, L-Zystein, alpha-Amino-beta-mercaptopropionic acid, L-, (R)-(+)-Cysteine, Cys, CHEMBL863, (2R)-2-amino-3-sulfanyl-propanoic acid, MFCD00064306, M03086, 4371-52-2, b-Mercaptoalanine, L-Cysteine hydrochloride hydrate, 202114-66-7, 3-mercapto-L-Alanine, EINECS 200-158-2, L-Cysteine from non-animal source, l-cycteine, racemic cysteine, L-Cysteine; Acetylcysteine Imp. B (EP); Acetylcysteine Impurity B, (2R)-2-amino-3-sulfanylpropanoic acid hydrochloride, UNII-K848JZ4886, 1ssq, S-Alkyl-L-cysteine, Ecolan (TN), S-alkyl-L-cysteines, L-Cysteine, 97%, β-Mercaptoalanine, H-Cys-OH HCl, CYSTEINE [HSDB], L-Cysteine (JP18), CYSTEINE [II], CYSTEINE [MI], CYSTEINE [VANDF], CYSTEINUM [HPUS], E-920, CYSTEINE [MART.], L-CYSTEINE [JAN], bmse000034, bmse000975, CYSTEINE [WHO-DD], Epitope ID:140791, Epitope ID:561431, L-CYSTEINE [FHFI], EC 200-158-2, L-CYSTEINE [VANDF], SCHEMBL3349, 2-Amino-3-mercaptopropionate, H-Cys-OH from animal source, GTPL4782, L-Cysteine, >=97%, FG, orb1304738, orb3025408, SCHEMBL5555288, L-2-Amino-3-mercaptopropanoate, L-Cysteine - non-animal origin, 2-amino-3-mercapto-, (R)-, SCHEMBL10603711, CHEBI:47915, MSK1405, AIDS002953, (R)-2-Amino-3-mercaptopropanoate, HY-Y0337, STR02584, (R)-2-amino-3-mercapto-propanoic acid, BDBM50109609, EBC-26052, s5635, (R)-2-Amino-3-mercaptopropanoic acid, propanoic acid, 2-amino-3-mercapto-, AKOS015854128, (+)-2-Amino-3-mercaptopropionic acid, CCG-266077, CS-W009027, DB00151, FC16020, FC76819, T2O2721, (R)-2-amino-3-mercapto-Propanoic acid, NCGC00248803-01, α-Amino-β-thiolpropionic acid, BP-14167, L-Cysteine, BioUltra, >=98.5% (RT), DB-297705, R-2-AMINO-3-MERCAPTOPROPIONIC ACID, L-Cysteine (Discontinued, See C4X-153235), L-Cysteine, SAJ special grade, >=98.5%, L-Cysteine, Vetec(TM) reagent grade, 97%, NS00008697, EN300-52823, ACETYLCYSTEINE IMPURITY B [EP IMPURITY], C00097, D00026, Propanoic acid, 2-amino-3-mercapto-, (R)-, L-Cysteine, Cell Culture Reagent (H-L-Cys-OH), Q186474, Q-201286, BBAE7AE6-FC21-4D37-808D-C7F7A2BA637F, BRD-K00795468-001-02-1, Q27115093, F0001-2369, F8880-8973, L-Cysteine, certified reference material, TraceCERT(R), Z760035162, Acetylcysteine EP Impurity B; Cysteine; Glutathione EP Impurity B, L-Cysteine, produced by Wacker Chemie AG, Burghausen, Germany, >=98.0%, L-Cysteine, from non-animal source, BioReagent, suitable for cell culture, >=98%, InChI=1/C7H6O5/c8-4-1-3(7(11)12)2-5(9)6(4)10/h1-2,8-10H,(H,11,12, 137657-43-3, 31387-49-2, alpha-amino-beta-mercaptopropionicacid;alpha-Amino-beta-thiolpropionic acid;alpha-amino-beta-thiolpropionicacid;half-cysteine;BETA-MERCAPTO-L-ALANINE;L-2-AMINO-3-MERCAPTOPROPANOIC ACID;L-beta-Mercaptoalanine;(R)-(+)-CYSTEINE

L-Cysteine is an α-amino acid with the chemical formula HO2CCH(NH2)CH2SH. 
L-Cysteine is a semi - essential amino acid, which means that it can be biosynthesized in humans. 
The thiol side chain in cysteine often participates in enzymatic reactions, serving as a nucleophile.

The thiol is susceptible to oxidization to give the disulfide derivative cystine, which serves an important structural role in many proteins. When used as a food additive, it has the E number E920.
L-Cysteine is a naturally occurring sulfur-containing amino acid with the formula C₃H₇NO₂S. 
It is one of the 20 standard amino acids found in proteins and is classified as a non-essential amino acid, meaning the human body can synthesize it from other compounds (mainly methionine and serine).

These bonds are crucial for stabilizing protein structure and enzyme function.
L-Cysteine improves protein folding and biological stability.
Physically, it is a white crystalline solid, slightly soluble in water, and sensitive to oxidation in air due to its sulfur group.

L-Cysteine can slowly convert to cystine when exposed to oxygen.
This improves understanding of its reactivity and storage behavior.
Functionally, L-cysteine is important in biochemistry, nutrition, and industrial applications, especially due to its role in detoxification pathways and as a precursor to antioxidants.

L-Cysteine is also involved in the production of glutathione, a major cellular antioxidant.
This improves cellular protection and metabolic balance.
L-Cysteine is best described as a biologically important sulfur amino acid used in protein synthesis, antioxidant production, and various food and pharmaceutical applications due to its reactive thiol group and reducing properties.

L-Cysteine is one of the 20 natural amino acids and, besides methionine,the only one which contains sulfur. 
It is a thiol-containing non-essential amino acid that is oxidized to form Cystine. 
It is a non-essential sulfur-containing amino acid in humans, related to cystine, Cysteine is important for protein synthesis, detoxification, and diverse metabolic functions.

Found in beta-keratin, the main protein in nails, skin, and hair, Cysteine is important in collagen production, as well as skin elasticity and texture. 
Also required in the manufacture of amino acid taurine, Cysteine is a component of the antioxidant glutathione, and plays a role in the metabolism of essential biochemicals such as coenzyme A, heparin, and biotin.
L-cysteine hydrochloride is used in the baking industry as dough conditioner. 

Specially, it breaks the disulfide bonds of gluten, which lowers the viscosity of the dough. 
L-Cysteine is then easier to work with and increases the elasticity of the dough, helping it to rise during baking.
L-cysteine is available through many dietary sources, primarily animal protein. Eggs and dairy products also contain significant levels of l-cysteine. 

L-Cysteine include broccoli, Brussels sprouts, garlic, granola, sprouted lentils, oats, onions and peppers. 
The commercial extraction of l-cysteine typically uses human hair, due to its high concentration of this amino acid. 
Other commercial sources include hog hair and poultry feathers. 

L-cysteine may also be synthesized in a process that involves fermentation by a variety of E. coli.
L-Cysteine is a semi-essential, sulfur-containing amino acid that your body uses to build proteins and synthesize glutathione, its primary antioxidant. 
While the body can produce it from methionine, dietary intake is vital for optimal health. 

L-Cysteine is widely used in wellness, clinical, and food manufacturing applications.
L-cysteine, also known as cysteine, is a non-essential amino acid of the human body. 
Amino acids are protein components and protein is the material basis of life. 

Ranging from human to microorganism, all consist of protein. 
Protein is composed of peptides, and peptide chain is composed of amino acids. 
Different proteins are composed of peptide chains in different order and length. 

Genes related to heredity are in fact amino acid chains in different orders.
L-cysteine is closely related to cysteine, and two molecules of cysteine can form a cysteine. 
L-Cysteine is relatively unstable and easy to become cysteine. 

L-Cysteine can also re-generate cysteine. 
These two both are sulfur-containing amino acids, which affect the formation of skin and can be used for detoxification.

L-Cysteine is a semiessential[7] proteinogenic amino acid with the formula HS−CH2−CH(NH2)−COOH. 
The thiol side chain in cysteine enables the formation of disulfide bonds, and often participates in enzymatic reactions as a nucleophile. 
L-Cysteine is chiral, but both D and L-cysteine are found in nature. 

L‑Cysteine is a protein monomer in all biota, and D-cysteine acts as a signaling molecule in mammalian nervous systems.
L-Cysteine is named after its discovery in urine, which comes from the urinary bladder or cyst, from Greek κύστις kýstis, "bladder".
L-Cysteine is encoded by the codons UGU and UGC.

Melting point: 240 °C (dec.) (lit.)
Boiling point: 293.9 ± 35.0 °C (Predicted)
alpha: 8.75º (c=12, 2N HCl)
Density: 1.197 (estimate)
bulk density: 300 kg/m3
FEMA: 3263 | L-CYSTEINE
refractive index: 8.8° (C=8, 1 mol/L HCl)
FLAVIS Number: 17.033 | L-Cysteine
storage temp.: Store below +30°C.
solubility: H2O: 25 mg/mL
form: Solid
pKa: 1.92 (at 25℃)
color: White
PH: 4.5–5.5 (100 g/L, H2O, 20℃)
Odor: sulfury
Odor Type: sulfurous
biological source: non-animal source
optical activity: Optical rotation: +8° to +9° (c = 5, 1 N HCl, 20°C)
Water Solubility: 280 g/L (25 ºC)
Sensitive: Air Sensitive
λmax:
λ: 260 nm, Amax: 1.5
λ: 280 nm, Amax: 0.2
Merck: 14,2781
JECFA Number: 1419
BRN: 1721408
Stability: Stable, but may be air sensitive. Incompatible with oxidizing agents, bases.
Cosmetics Ingredients Functions: REDUCING; HAIR CONDITIONING; FRAGRANCE; ANTISTATIC; HAIR WAVING OR STRAIGHTENING; ANTIOXIDANT
Cosmetic Ingredient Review (CIR): L-Cysteine (52-90-4)
InChI: 1S/C3H7NO2S/c4-2(1-7)3(5)6/h2,7H,1,4H2,(H,5,6)/t2-/m0/s1
InChIKey: XUJNEKJLAYXESH-REOHCLBHSA-N
SMILES: NC@@HC(O)=O
LogP: -2.49

L‑Cysteine is a sulfur-containing amino acid that constitutes protein. 
L‑Cysteine has an ionized mercapto side chain and is hydrophobic. 
However, it is unstable in neutral pH or alkaline pH in the air, and its aqueous solution can automatically convert into cysteine.

Although cystine does not belong to the list of amino acids composing protein, but in the process of protein conformation, it can generate by oxidizing the SH group of two close cysteine, so many protein molecules in the body contain cystine. 
The formation of cystine disulfide bond makes the protein conformation more stable. 
Of course, if the cystine is reduced, it can also produce two molecules of cysteine.

L-cysteine is an optically active form of cysteine having L-configuration. 
L‑Cysteine has a role as a flour treatment agent, a human metabolite and an EC 4.3.1.3 (histidine ammonia-lyase) inhibitor. 
It is a serine family amino acid, a proteinogenic amino acid, a cysteine and a L-alpha-amino acid. 

L‑Cysteine is a conjugate base of a L-cysteinium. 
It is a conjugate acid of a L-cysteinate(1-). 
L‑Cysteine is an enantiomer of a D-cysteine. 

L‑Cysteine is a tautomer of a L-cysteine zwitterion.
L‑Cysteine is a mercapto-containing aliphatic neutral amino acid. 
It is colorless crystal with isoelectric point of 5.07, PK1 = 1.71, pK2 = 8.33, and pK3 = 10.78. 

L‑Cysteine is Soluble in water, ethanol, acetic acid and ammonia, while not soluble in benzene, carbon tetrachloride, ethyl acetate, carbon disulfide, ether and acetone. 
L-cysteine is an essential component of the protein and can be synthesized from serine or methionine in animals. 
L-cysteine comes to decompose while heated to 240 ° C, and can be quickly oxidized by air to form cystine in neutral or slightly alkaline solution. 

The acid solution of L-cysteine can be stored for several days, and stored better under the protection of nitrogen. 
The aqueous solution of levorotatory L-cysteine changes into dark blue after adding ferric chloride. 
It can be produced by the degradation of cystine, and also can be obtained by the hydrochloric acid hydrolysis, copper oxide treatment and then hydrogen sulfide decomposition of human hair and other silkworm. 

L-cysteine can be used for anti-radiation and the treatment of radiation sickness, as well as for hepatitis, liver poisoning, radiopharmaceutical poisoning, acrylonitrile and antimony poisoning and allergic diseases in medicine. 
L‑Cysteine can also be applied for the biochemical and nutritional research. 
Pyruvate and mercaptoethanamine are its general catabolites. 

It is involved in the synthesis of glutathione, taurine and so on. 
The disulfide bridge in the polypeptide chain is also formed by dehydrogenation and condensation of two molecules of cysteine.
Some foods considered rich in cysteine include poultry, eggs, beef, and whole grains. 

In high-protein diets, cysteine may be partially responsible for reduced blood pressure and stroke risk.
Although classified as a nonessential amino acid, in rare cases, cysteine may be essential for infants, the elderly, and individuals with certain metabolic diseases or who suffer from malabsorption syndromes. 
L‑Cysteine can usually be synthesized by the human body under normal physiological conditions if a sufficient quantity of methionine is available.

L-cysteine plays a key role in protein structure stabilization, because its thiol groups can form disulfide bridges, which act like molecular “locks” that hold proteins in their correct 3D shape.
This is especially important in enzymes and structural proteins like keratin.
L‑Cysteine improves protein stability and biological function.

In human metabolism, L-cysteine is involved in the synthesis of glutathione, one of the body’s most important antioxidants, which helps neutralize reactive oxygen species (ROS) and protect cells from oxidative stress.
It also supports liver detoxification processes.
L‑Cysteine improves antioxidant defense and detoxification capacity.

L‑Cysteine is used as a dough conditioner in baking because it breaks some disulfide bonds in gluten proteins, making dough more extensible and easier to process.
This is especially important in industrial bread production.
L‑Cysteine improves dough handling and bakery efficiency.

In pharmaceutical and medical research, L-cysteine is used in formulations and studies related to mucolytic agents (substances that thin mucus) and antioxidant therapies.
It is also a precursor to compounds used in detoxification treatments.
L‑Cysteine improves therapeutic development and biomedical applications.

In cosmetics and personal care, it is sometimes used in hair treatment products because sulfur compounds are important for keratin structure in hair and nails.
It can contribute indirectly to hair strength and repair formulations.
This improves cosmetic hair care performance.

In cell culture and biotechnology, L-cysteine is added to growth media because it supports cell metabolism and helps maintain redox balance in controlled environments.
It is important in microbiology and pharmaceutical production.
L‑Cysteine improves cell growth and bioprocess stability.

In industrial synthesis, L-cysteine is produced on a large scale either by extraction from protein hydrolysates or via microbial fermentation, making it widely available for food and pharmaceutical use.
Modern production often prefers fermentation for purity and sustainability.
L‑Cysteine improves manufacturing efficiency and scalability.

In environmental chemistry, sulfur-containing amino acids like L-cysteine participate in natural sulfur cycling and can influence the formation of sulfur-containing organic compounds in ecosystems.
This connects biological systems with environmental chemistry.
L‑Cysteine improves biogeochemical understanding.

Uses Of L‑Cysteine:
L-cysteine can be used as bread improver, nutritional supplements, antioxidants and color fixative. 
It can also be applied for curing acrylonitrile and aromatic acid poisoning, preventing radiation damage and treating bronchitis and phlegm. 
L-cysteine can absorb alcohol and convert it into acetaldehyde to alleviate a hangover.

L-cysteine can be used for the treatment of eczema, urticaria, freckles and other skin diseases. 
And its series products are widely used in medicine, food and cosmetics industry
L-cysteine can be used for biochemical research and as the antidote for hepatitis, liver poisoning, radiopharmaceutical poisoning, antimony poisoning, etc.

L-cysteine is mainly used for medicine, cosmetics, biochemical research and so on. 
It can be used in the bread material to accelerate the formation of gluten and to promote fermenting and depanning, as well as to prevent aging. 
L‑Cysteine can be used in natural fruit juices to prevent oxidation of vitamin C and to prevent fruit juice from becoming brown. 

L‑Cysteine has detoxification effect and can be used for curing acrylonitrile poisoning and aromatic acidosis. 
This product also has the role of preventing the human body from radiation damage. 
L‑Cysteine can be used as bronchitis drugs, especially as phlegm drugs (mostly in the form of acetyl L-cysteine methyl ester salt). 

In cosmetics, it is mainly used as cosmetic water, perm solution, anti-sun cream and other skin care.
L-cysteine can be used as the receptor agonists of NMDA glutamate.
L-Cysteine is a non-essential amino acid that can be synthesized by the human body under normal physiological conditions if a sufficient quantity of methionine is available. 

L-Cysteine is commonly used as a precursor in the food and pharmaceutical industries. 
L-Cysteine is used as a processing aid for baking, as an additive in cigarettes, as well as in the preparation of meat flavours. 
It is used in foods to prevent oxygen from destroying vitamin c and is used in doughs to reduce mixing time.

L-cysteine is mainly used as a food additive, dough conditioner, pharmaceutical intermediate, and biochemical reagent because of its reducing properties and role in protein chemistry.
In baking industry, it is used as a dough conditioner.
This improves dough elasticity and processing efficiency.

In pharmaceutical production, it is used as an intermediate and antioxidant-related compound.
This improves drug formulation and biochemical stability.
In food processing, it is used to modify protein structure in industrial food production.

This improves texture and processing control.
In cosmetics and personal care, it is used in hair and skin-related formulations.
This improves product performance and keratin support.

In biotechnology and research, it is used in cell culture media and laboratory studies.
This improves experimental reliability and cell growth conditions.
L-Cysteine is mainly used as a food additive, dough conditioner, pharmaceutical intermediate, and biochemical reagent because of its reducing (disulfide-breaking) ability and its role in protein chemistry and metabolism.

In industrial baking (bread, pastries, dough products), it is used as a dough conditioner to modify gluten structure by breaking disulfide bonds in wheat proteins.
L‑Cysteine makes dough softer, more elastic, and easier to process in high-speed industrial production.
This improves dough handling and baking efficiency.

In processed food manufacturing, it is used to improve texture and processing performance in products made from wheat flour and protein-rich mixtures.
L‑Cysteine helps standardize dough behavior in large-scale production.
This improves consistency and production control.

In pharmaceutical production, it is used as an intermediate in drug synthesis and in formulations related to antioxidant systems and mucolytic agents (mucus-thinning compounds such as related derivatives).
It also supports biochemical stability in some preparations.
L‑Cysteine improves drug development and formulation chemistry.

In cosmetics and personal care products, it is used in hair-care formulations (shampoos, treatments) because sulfur compounds are important for keratin structure in hair and nails.
It helps support conditioning and structural protein care systems.
L‑Cysteine improves hair strength and cosmetic performance.

In biotechnology and cell culture media, it is used as a nutrient and redox-balancing component that helps maintain a healthy cellular environment for growth and protein expression.
L‑Cysteine supports cellular metabolism and antioxidant balance.
This improves cell culture stability and research reliability.

In animal feed and nutrition, it can be used in amino acid supplementation to support protein synthesis and metabolic functions in livestock.
It helps balance sulfur amino acid content in feed formulations.
L‑Cysteine improves feed quality and nutritional efficiency.

In chemical and laboratory applications, it is used as a reducing agent in biochemical experiments, especially in protein chemistry where disulfide bond reduction is needed.
It helps study protein structure and folding mechanisms.
L‑Cysteine improves experimental control and molecular analysis.

In industrial fermentation and bioprocessing, it is used to support microbial growth and metabolic pathways that require sulfur-containing amino acids.
L‑Cysteine helps maintain redox balance in production systems.
L‑Cysteine improves bioprocess efficiency and yield.

Safety Profile Of L‑Cysteine:
Moderately toxic by ingestion, intraperitoneal, and subcutaneous routes. 
Experimental reproductive effects. 
Human mutation data reported when heated to decomposition fumes of SO and NO.

L-Cysteine is generally considered a low-toxicity and relatively safe amino acid, especially at the levels used in food, pharmaceuticals, and cosmetics. 
However, hazards can occur mainly from high doses, impurities, or industrial handling conditions.
The main hazard is mild irritation, particularly from dust or concentrated solutions.

L‑Cysteine may cause slight irritation to the eyes, skin, or respiratory tract in industrial settings where powders are handled.
This improves workplace exposure awareness.
Inhalation of L-cysteine dust can cause temporary respiratory irritation, such as coughing or throat discomfort, especially without proper ventilation.

L‑Cysteine is mainly a physical irritation rather than chemical toxicity.
L‑Cysteine improves occupational safety control.
Eye contact may lead to stinging or irritation, particularly with solid particles or concentrated solutions.

Rinsing with water is typically sufficient for first aid.
This improves basic handling safety.
From a biochemical perspective, very high intake of L-cysteine supplements may potentially disrupt amino acid balance and metabolic pathways, although such effects are rare under normal dietary exposure.

Excess sulfur amino acid intake may place additional metabolic load on the liver.
L‑Cysteine improves nutritional safety awareness.
In sensitive individuals, high doses of cysteine-related supplements have been associated with gastrointestinal discomfort, such as nausea or stomach upset.

L‑Cysteine is generally dose-dependent and reversible.
This improves supplement usage caution.
From a chemical stability standpoint, L-cysteine can oxidize in air to form cystine, which is not dangerous but indicates reduced stability and potential loss of activity in formulations.