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Amino acids and derivatives

L-(+)-Cysteine

Also known as L-cysteine, cysteine, Cystein

CAS 52-90-4Formula C3H7NO2SMolar mass 121.16 g/molEC 200-158-2
GHS signal word: Warning. Pictograms: Harmful or irritant 191 suppliers listed Drug substance
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L-(+)-Cysteine chemical structure, C3H7NO2S, CAS 52-90-4
2D chemical structure

Key facts

What buyers check first

All properties
Appearance
Colorless crystals
Melting point
260 °C
Solubility
Freely soluble in water
HS code
293090
Category
Amino acids and derivatives
Illustrative photo, colourless crystals beside an amber glass bottle on a laboratory bench
Typical packagingIllustrative packaging image, not the actual product

What is L-(+)-Cysteine?

Plain description, key identifiers and synonyms

L-cysteine is an optically active form of cysteine having L-configuration. It has a role as a flour treatment agent, an EC 4.3.1.3 (histidine ammonia-lyase) inhibitor and a human metabolite. It is a cysteine, a L-alpha-amino acid, a serine family amino acid and a proteinogenic amino acid. It is a conjugate base of a L-cysteinium. It is a conjugate acid of a L-cysteinate(1-). It is an enantiomer of a D-cysteine. It is a tautomer of a L-cysteine zwitterion.

L-(+)-Cysteine is a sulfur-containing amino acid.

Identifiers

Registry numbers, names and line notations, tap to copy

IUPAC name
(2R)-2-amino-3-sulfanylpropanoic acid
CAS number
52-90-4 CAS number cross-checkedOther or deprecated CAS: 202114-66-7, 4371-52-2
EC number
200-158-2
Molecular formula
C3H7NO2S
UNII
K848JZ4886
MDL number
MFCD00064306
INCI name
CYSTEINE
InChIKey
XUJNEKJLAYXESH-REOHCLBHSA-N
InChI
InChI=1S/C3H7NO2S/c4-2(1-7)3(5)6/h2,7H,1,4H2,(H,5,6)/t2-/m0/s1
Canonical SMILES
NC(CS)C(=O)O
Isomeric SMILES
C([C@@H](C(=O)O)N)S

Synonyms

  • L-cysteine
  • cysteine
  • Cystein
  • (R)-2-Amino-3-mercaptopropanoic acid
  • Thioserine
  • Half-cystine
  • beta-Mercaptoalanine
  • L-Cystein
  • (2R)-2-amino-3-sulfanylpropanoic acid
  • Cysteinum
  • L-Cys
  • cisteina
  • Half cystine
  • 2-Amino-3-mercaptopropionic acid
  • L-Alanine, 3-mercapto-
  • Free cysteine
  • Cisteinum
  • 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-
  • alpha-Amino-beta-mercaptopropanoic acid, L-
  • Propanoic acid, 2-amino-3-mercapto-, (R)-
Show all 37 synonyms
  • 2-Amino-3-mercaptopropanoic acid, (R)-
  • 2-amino-3-mercaptopropanoate
  • Cisteinum (Latin)
  • (2R)-2-amino-3-mercaptopropanoate
  • (2R)-2-amino-3-sulfanylpropanoate
  • l-cysteinum
  • l-cystAine
  • L-Cysteine High
  • 2-azaniumyl-3-sulfanylpropanoate
  • L-Cysteine 7403
  • L-Cysteine High 7404
  • (R)-2-Amino-3-sulfanyl-propanoic acid

Physical and chemical properties

Measured values and descriptors computed from the structure

Physical and chemical properties

Measured values, check the supplier specification for your grade

Appearance
Colorless crystalsexp.
Melting point
260 °Cexp.
Solubility
Freely soluble in waterexp.

Values vary by grade. Ask suppliers for the COA or TDS of the batch you buy.

Computed descriptors

Calculated from the structure, useful for screening and formulation

Molecular weight
121.16 g/molcalc.
Exact mass
121.0197 Dacalc.
LogP (octanol/water)
-0.67calc.
Topological polar surface area
63.32 Ųcalc.
Hydrogen bond donors
3calc.
Hydrogen bond acceptors
3calc.
Rotatable bonds
2calc.
Heavy atoms
7calc.
Rings
0calc.
Aromatic rings
0calc.
Fraction sp3 carbons
0.67calc.
Formal charge
0calc.
Stereocentres
1calc.
Lipinski rule of five
Passes (0 violations)calc.

Calculated for screening. Confirm critical figures with the supplier.

Safety and hazards

GHS classification summary, not a safety data sheet

GHS signal word
Warning
GHS07: Harmful or irritant
Harmful or irritant

Hazard statements

  • H302Harmful if swallowed.
  • H315Causes skin irritation.
  • H319Causes serious eye irritation.
  • H335May cause respiratory irritation.
Precautionary statements (19)
  • P261Avoid breathing dust, fume, gas, mist, vapours or spray.
  • P264Wash skin thoroughly after handling.
  • P264 + P265Wash skin thoroughly after handling. Do not touch eyes.
  • P270Do not eat, drink or smoke when using this product.
  • P271Use only outdoors or in a well-ventilated area.
  • P280Wear protective gloves, protective clothing, eye protection and face protection.
  • P301 + P317If swallowed: Get medical help.
  • P302 + P352If on skin: Wash with plenty of water.
  • P304 + P340If inhaled: Remove person to fresh air and keep comfortable for breathing.
  • P305 + P351 + P338If in eyes: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing.
  • P319Get medical help if you feel unwell.
  • P321Specific treatment (see supplemental first aid instructions on the label).
  • P330Rinse mouth.
  • P332 + P317If skin irritation occurs: Get medical help.
  • P337 + P317If eye irritation persists: Get medical help.
  • P362 + P364Take off contaminated clothing. And wash it before reuse.
  • P403 + P233Store in a well-ventilated place. Keep container tightly closed.
  • P405Store locked up.
  • P501Dispose of contents and container in accordance with local regulations.

GHS classification summary, not a safety data sheet (SDS). Classifications can differ by supplier, grade and concentration. Always check the supplier's SDS.

Full safety data and first aid

L-(+)-Cysteine suppliers

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All 191 suppliers
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Where suppliers are based

191 suppliers in 26 countries

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L-(+)-Cysteine price

Indicative price range per kg from live supplier offers

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Uses and applications

What the substance is used for, by industry and function

Reported uses (ppm):

Table: Reported uses (ppm): (Flavor and Extract Manufacturers' Association, 1994) [Table#3867].

Biochemical and nutrition research, reducing agent in bread doughs (up to 90 ppm).

Veterinary medication:.

Treatment with cysteine reduced seedling injury caused by gamma-irradiation of sorghum seed. Cysteine effects were most pronounced in primary root elongation.

Use classes: Cosmetics.

Cosmetic ingredient, INCI name CYSTEINE(antioxidant, antistatic, hair conditioning, hair waving or straightening)

Roles

  • additive
  • animal metabolite
  • enzyme inhibitor
  • eukaryotic metabolite
  • flour treatment agent
  • food additive
  • food component
  • fundamental metabolite
  • human metabolite
  • mammalian metabolite
  • metabolite
  • physiological role

Functional uses

  • Filler
  • Flavouring and nutrient
  • Food preservative
  • Processing aids not otherwise specified

Cosmetic functions

  • Antioxidant
  • Antistatic
  • Fragrance
  • Hair conditioning
  • Hair waving or straightening
  • Reducing

Pharmacology

Cysteine 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. (NCI04)

How it is made

By addition of a thiol compound to an unsaturated amino acid derivative, by hydrolysis of proteins in the presence of carbon dioxide, by treating in HCl hydrolysis of proteins in the presence of carbon dioxide, by treating an HCl hydrolysate of hair with CuO2, followed by the decomposition of the resulting copper-cysteine complex with hydrogen sulfide, by the addition of thioacetic acid to alpha-acetamido acrylic acid, by treatment of a keratine HCl hydrolysate with zinc to reduce the cystine present to cysteine, by electrolytic reduction of cystine.

L-Cysteine used to be produced almost exclu

Read more

sively by hydrolysis of hair or other keratins. The amino acid isolated was l-cystine, which was reduced electrolytically to l-cysteine. L-Cysteine has also been prepared from beta-chloro-d,l-alanine and sodium sulfide with cysteine desulfhydrase, an enzyme obtained from, e.g., Citrobacterium freundii. Today, however, the main processes for cysteine production are biological. A direct fermentation process has been developed for the manufacture of l-cystine, using a modified Escherichia coli bacterium. The technology has been extended to prepare other modified l-cysteine analogues. An enzymatic process for l-cysteine has been successfully developed using microorganisms capable to hydrolyze 2-amino-delta2-thiazoline 4-carboxylic acid (ATC) which is readily available from methyl alpha-chloroacrylate and thiourea.

Regulatory status

Inventories, regulations and trade controls that list this substance

Health and food

  • EU cosmetic ingredient inventory
  • Active ingredient in FDA approved drug labels

United States

  • TSCA inventory (USA)
    Status: Active in US commerce

HS code and trade data

Customs classification and reported world trade statistics

Global trade

World import and export statistics for the HS code L-(+)-Cysteine is traded under.

HS 2930.90Indicative HS code

Organo-sulphur compounds, other

World exports in 2024
$5.83B
+0.1% vs 2023, imports $5.93B
2019 to 2024
Top exporters
  1. China40.7%
  2. United States10.9%
  3. Japan9.3%
Top importers
  1. United States13.3%
  2. Brazil12.6%
  3. China6.6%
Reported customs values in USD, not prices.Full trade data

The HS code shown for L-(+)-Cysteine is indicative (it was assigned by structure rules). Confirm the classification with your customs broker before shipping.

Frequently asked questions

Quick answers about L-(+)-Cysteine, based on the data on this page

What is L-(+)-Cysteine?

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

What is the CAS number of L-(+)-Cysteine?

The CAS registry number of L-(+)-Cysteine is 52-90-4. Other or deprecated CAS numbers: 202114-66-7, 4371-52-2.

What is the molecular formula and weight of L-(+)-Cysteine?

The molecular formula of L-(+)-Cysteine is C3H7NO2S and its molar mass is 121.16 g/mol.

What is L-(+)-Cysteine used for?

Reported uses (ppm): Table: Reported uses (ppm): (Flavor and Extract Manufacturers' Association, 1994) [Table#3867]. Biochemical and nutrition research, reducing agent in bread doughs (up to 90 ppm). Veterinary medication:. Treatment with cysteine reduced seedling injury caused by gamma-irradiation of sorghum seed.

Is L-(+)-Cysteine hazardous?

L-(+)-Cysteine carries the GHS signal word "Warning". Main hazards: harmful if swallowed, causes skin irritation, causes serious eye irritation. This summary is not an SDS, always read the supplier safety data sheet.

What is the HS code of L-(+)-Cysteine?

L-(+)-Cysteine is usually classified under HS code 293090 (Organo-sulphur compounds, other). This is indicative, confirm it with your customs broker before shipping.

Where can I buy L-(+)-Cysteine?

CompoundList lists 191 suppliers of L-(+)-Cysteine in China, United States, India, Germany and 22 more. Send one free request to get and compare quotes. Your contact details stay private until you accept a quote.

Where can I buy L-(+)-Cysteine in India?

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What is the price of L-(+)-Cysteine?

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Guides for buyers

Practical guides that help when you source, ship or handle L-(+)-Cysteine

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Data last updated 7 Oct 2026. Details may have changed, please confirm them with the supplier. Report an error on this page
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