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2D Structure
Also known as: L-cysteine, 52-90-4, (r)-2-amino-3-mercaptopropanoic acid, Thioserine, Cystein, Half-cystine
Molecular Formula
C3H7NO2S
Molecular Weight
121.16  g/mol
InChI Key
XUJNEKJLAYXESH-REOHCLBHSA-N
FDA UNII
K848JZ4886

A thiol-containing non-essential amino acid that is oxidized to form CYSTINE.
1 2D Structure

2D Structure

2 Identification
2.1 Computed Descriptors
2.1.1 IUPAC Name
(2R)-2-amino-3-sulfanylpropanoic acid
2.1.2 InChI
InChI=1S/C3H7NO2S/c4-2(1-7)3(5)6/h2,7H,1,4H2,(H,5,6)/t2-/m0/s1
2.1.3 InChI Key
XUJNEKJLAYXESH-REOHCLBHSA-N
2.1.4 Canonical SMILES
C(C(C(=O)O)N)S
2.1.5 Isomeric SMILES
C([C@@H](C(=O)O)N)S
2.2 Other Identifiers
2.2.1 UNII
K848JZ4886
2.3 Synonyms
2.3.1 MeSH Synonyms

1. Cysteine Hydrochloride

2. Half Cystine

3. Half-cystine

4. L Cysteine

5. L-cysteine

6. Zinc Cysteinate

2.3.2 Depositor-Supplied Synonyms

1. L-cysteine

2. 52-90-4

3. (r)-2-amino-3-mercaptopropanoic Acid

4. Thioserine

5. Cystein

6. Half-cystine

7. (r)-cysteine

8. L-(+)-cysteine

9. L-cystein

10. (2r)-2-amino-3-sulfanylpropanoic Acid

11. H-cys-oh

12. Cysteinum

13. Cysteine, L-

14. Beta-mercaptoalanine

15. Half Cystine

16. Free Cysteine

17. L-cys

18. L-alanine, 3-mercapto-

19. (r)-2-amino-3-mercaptopropionic Acid

20. Cisteinum [latin]

21. Cysteine [inn]

22. Fema No. 3263

23. L-2-amino-3-mercaptopropionic Acid

24. Cisteina [spanish]

25. Cisteina

26. Cisteinum

27. L Cysteine

28. L-zystein

29. Alpha-amino-beta-thiolpropionic Acid

30. L-2-amino-3-mercaptopropanoic Acid

31. Cysteinum [inn-latin]

32. Cisteina [inn-spanish]

33. Beta-mercaptoalanine, L-

34. (2r)-2-amino-3-mercaptopropanoic Acid

35. Nsc-8746

36. 2-amino-3-mercaptopropionic Acid

37. Ccris 912

38. Chebi:17561

39. Hsdb 2109

40. Alpha-amino-beta-thiolpropionic Acid, L-

41. Ai3-26559

42. Alpha-amino-beta-mercaptopropanoic Acid, L-

43. Alpha-amino-beta-mercaptopropionic Acid, L-

44. Propanoic Acid, 2-amino-3-mercapto-, (r)-

45. 2-amino-3-mercaptopropanoic Acid, (r)-

46. Cysteine Hcl

47. (r)-(+)-cysteine

48. E 920

49. Cys

50. Chembl863

51. E920

52. Mfcd00064306

53. K848jz4886

54. (+)-2-amino-3-mercaptopropionic Acid

55. 4371-52-2

56. Polycysteine

57. B-mercaptoalanine

58. Nsc 8746

59. (2r)-2-amino-3-mercaptopropanoate

60. (2r)-2-amino-3-sulfanylpropanoate

61. 3-mercapto-l-alanine

62. 202114-66-7

63. Einecs 200-158-2

64. L-cycteine

65. Racemic Cysteine

66. 2-amino-3-mercaptopropanoate

67. Unii-k848jz4886

68. 1ssq

69. Ecolan (tn)

70. L-cysteine, 97%

71. .beta.-mercaptoalanine

72. (2r)-2-amino-3-sulfanyl-propanoic Acid

73. 1xt8

74. Cysteine [hsdb]

75. Cysteine [inci]

76. L-cysteine (jp17)

77. Cysteine [ii]

78. Cysteine [mi]

79. Cysteine [vandf]

80. Cysteinum [hpus]

81. Cysteine [mart.]

82. L-cysteine [jan]

83. Bmse000034

84. Bmse000975

85. Cysteine [who-dd]

86. Epitope Id:140791

87. L-cysteine [fhfi]

88. L-cysteine-[1-13c]

89. Ec 200-158-2

90. L-cysteine [vandf]

91. 2-amino-3-mercaptopropionate

92. Gtpl4782

93. L-cysteine, >=97%, Fg

94. L-2-amino-3-mercaptopropanoate

95. 2-amino-3-mercapto-, (r)-

96. Dtxsid8022876

97. L-cysteine From Non-animal Source

98. Aids002953

99. Zinc895042

100. (r)-2-amino-3-mercaptopropanoate

101. Hy-y0337

102. Str02584

103. (r)-2-amino-3-mercapto-propanoate

104. Bdbm50109609

105. S5635

106. (r)-2-amino-3-mercaptopropanoicacid

107. Akos015854128

108. Am81648

109. Ccg-266077

110. Cs-w009027

111. Db00151

112. (r)-2-amino-3-mercapto-propanoic Acid

113. Ncgc00248803-01

114. .alpha.-amino-.beta.-thiolpropionic Acid

115. L-cysteine, Bioultra, >=98.5% (rt)

116. R-2-amino-3-mercaptopropionic Acid

117. E-920

118. L-cysteine, Saj Special Grade, >=98.5%

119. L-cysteine, Vetec(tm) Reagent Grade, 97%

120. Acetylcysteine Impurity B [ep Impurity]

121. C-9615

122. C00097

123. D00026

124. M03086

125. Propanoic Acid, 2-amino-3-mercapto-, (r)-

126. L-cysteine, Cell Culture Reagent (h-l-cys-oh)

127. 064c306

128. Q186474

129. (2r)-2-amino-3-sulfanylpropanoic Acid Hydrochloride

130. Q-201286

131. Q-201328

132. Bbae7ae6-fc21-4d37-808d-c7f7a2ba637f

133. Q27115093

134. F0001-2369

135. F8880-8973

136. L-cysteine, Certified Reference Material, Tracecert(r)

137. L-cysteine, Produced By Wacker Chemie Ag, Burghausen, Germany, >=98.0%

138. L-cysteine, From Non-animal Source, Bioreagent, Suitable For Cell Culture, >=98%

139. L-cysteine, Pharmagrade, From Non-animal Source, Ajinomoto, Manufactured Under Appropriate Gmp Controls For Pharma Or Biopharmaceutical Production, Suitable For Cell Culture

2.4 Create Date
2004-09-16
3 Chemical and Physical Properties
Molecular Weight 121.16 g/mol
Molecular Formula C3H7NO2S
XLogP3-2.5
Hydrogen Bond Donor Count3
Hydrogen Bond Acceptor Count4
Rotatable Bond Count2
Exact Mass121.01974964 g/mol
Monoisotopic Mass121.01974964 g/mol
Topological Polar Surface Area64.3 Ų
Heavy Atom Count7
Formal Charge0
Complexity75.3
Isotope Atom Count0
Defined Atom Stereocenter Count1
Undefined Atom Stereocenter Count0
Defined Bond Stereocenter Count0
Undefined Bond Stereocenter Count0
Covalently Bonded Unit Count1
4 Drug and Medication Information
4.1 Therapeutic Uses

/EXPL THER/ Acetaminophen-cysteine adducts (APAP-CYS) are a serum biomarker of acetaminophen exposure, formed when the oxidative metabolite of acetaminophen binds to cysteine residues of hepatic proteins. APAP-CYS adducts become elevated in cases of acute liver failure following acetaminophen overdose and have been proposed as a diagnostic tool to identify acetaminophen-induced acute liver failure when standard testing is inconclusive.

PMID:25896948 Full text: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4469719 Frey SM et al; J Med Toxicol 11 (2): 218-22 (2015)


/EXPL THER/ Lead is a toxic heavy metal that adversely affects nervous tissues; it often occurs as an environmental pollutant. We investigated histological changes in the cerebral cortex, hippocampus and cerebellum of adult albino mice following exposure to lead acetate. We also studied the possible ameliorative effect of the chelating agent, L-cysteine, on lead-induced neurotoxicity. We divided albino mice into six groups: 1) vehicle-only control, 2) L-cysteine control, 3 and 4) treated for 7 days with 20 and 40 mg/kg lead acetate, respectively, and 5 and 6) treated for 7 days with 20 and 40 mg/kg lead acetate, respectively, followed by 50 mg/kg L-cysteine for 7 days. Lead acetate administration caused disorganization of cell layers, neuronal loss and degeneration, and neuropil vacuolization. Brain sections from lead-intoxicated mice treated with L-cysteine showed fewer pathological changes; the neuropil showed less vacuolization and the neurons appeared less damaged. L-cysteine at the dose we used only marginally alleviated lead-induced toxicity.

PMID:27045382 Mahmoud YI, Sayed SS; Biotech Histochem 1-6 (2016) (Epub ahead of print)


/EXPL THER/ In hamster lung cell cultures addn of l-Cysteine or vit C to media protects against or reverses abnormal growth & malignant transformation in aged controls (1-2 yr old) or young (3-6 mo) after repeated exposure to smoke of tobacco or marijuana cigarettes.

Leuchtenberger C; Br J Exp Pathol 58 (6): 625-34 (1977)


/EXPL THER/ L-Cysteine admin orally or ip to rats protected against acute toxicity of methylmercury chloride, reducing mercury content in kidney & brain but not in liver.

Sugiyama et al; Toho Igakkai Zasshi 22 (1): 78-85 (1975)


For more Therapeutic Uses (Complete) data for CYSTEINE (7 total), please visit the HSDB record page.


4.2 Drug Indication

For the prevention of liver damage and kidney damage associated with overdoses of acetaminophen


5 Pharmacology and Biochemistry
5.1 Pharmacology

Due to this ability to undergo redox reactions, cysteine has antioxidant properties. Cysteine is an important source of sulfur in human metabolism, and although it is classified as a non-essential amino acid, cysteine may be essential for infants, the elderly, and individuals with certain metabolic disease or who suffer from malabsorption syndromes. Cysteine may at some point be recognized as an essential or conditionally essential amino acid.


5.2 Metabolism/Metabolites

L-Cysteine is the central compound in sulfur metabolism in the human body. In proteins the formation of disulfide bonds between the thiol groups of cysteine plays an important role for tertiary structure and enzymatic activity; cysteine is however always incorporated in the polypeptide chain as cysteine. L-Cysteine is degraded to pyruvate in two steps: one is removal of sulfur and the other is a transamination. Cysteine can be metabolized to form taurine and carbon dioxide through the cysteinsulfinate pathway, where the initial step is oxidation of cysteine to cysteine sulfinate. This step is catalyzed by cysteine dioxygenase. Cysteine sulfinate may then be decarboxylated to form taurine or it may be metabolized via the putative intermediate beta-sulfinylpyruvate to pyruvate and sulfite and then to carbon dioxide and sulfate.

European Chemicals Agency (ECHA); Registered Substances, L-cysteine (CAS Number: 52-90-4) (EC Number: 200-158-2) (Last updated: May 17, 2016). Available from, as of May 24, 2016: https://echa.europa.eu/


Amino acid catabolism is essential for adjusting pool sizes of free amino acids and takes part in energy production as well as nutrient remobilization. The carbon skeletons are generally converted to precursors or intermediates of the tricarboxylic acid cycle. In the case of cysteine, the reduced sulfur derived from the thiol group also has to be oxidized in order to prevent accumulation to toxic concentrations. Here we present a mitochondrial sulfur catabolic pathway catalyzing the complete oxidation of L-cysteine to pyruvate and thiosulfate. After transamination to 3-mercaptopyruvate the sulfhydryl group from L-cysteine is transferred to glutathione by sulfurtransferase 1 and oxidized to sulfite by the sulfur dioxygenase ETHE1. Sulfite is then converted to thiosulfate by addition of a second persulfide group by sulfurtransferase 1. This pathway is most relevant during early embryo development and for vegetative growth under light limiting conditions. Characterization of a double mutant produced from Arabidopsis thaliana T-DNA insertion lines for ETHE1 and sulfurtransferase 1 revealed that an intermediate of the ETHE1 dependent pathway, most likely a persulfide, interferes with amino acid catabolism and induces early senescence.

PMID:27105581 Hofler S et al; Physiol Plant doi: 10.1111/ppl.12454 (2016) (Epub ahead of print)


5.3 Mechanism of Action

Cysteine can usually be synthesized by the human body under normal physiological conditions if a sufficient quantity of methionine is available. Cysteine is typically synthesized in the human body when there is sufficient methionine available. Cysteine exhibits antioxidant properties and participates in redox reactions. Cysteine's antioxidant properties are typically expressed in the tripeptide glutathione, which occurs in humans as well as other organisms. Glutathione (GSH) typically requires biosynthesis from its constituent amino acids, cysteine, glycine, and glutamic acid, due to its limited systemic availability. Glutamic acid and glycine are readily available in the diets of most industrialized countries, but the availability of cysteine can be the limiting substrate. In human metabolism, cysteine is also involved in the generation of sulfide present in iron-sulfur clusters and nitrogenase by acting as a precursor. In a 1994 report released by five top cigarette companies, cysteine is one of the 599 additives to cigarettes. Its use or purpose, however, is unknown, like most cigarette additives. Its inclusion in cigarettes could offer two benefits: Acting as an expectorant, since smoking increases mucus production in the lungs; and increasing the beneficial antioxidant glutathione (which is diminished in smokers).