Cysteine

Cysteine (symbol Cys or C; /ˈsɪstɪiːn/) is a semiessential proteinogenic amino acid with the formula HOOC−CH(−NH2)−CH2−SH. The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile. Cysteine is chiral, but interestingly, both D and L-cysteine are found in nature with D-cysteine having been found in developing brain (see Semenza et al., 2021).

Not to be confused with cytosine, cystine, cytisine, cytidine, or Sistine.
"Cys" redirects here. For other uses, see Cys (disambiguation).
l-Cysteine

Skeletal formula of L-cysteine
Names
IUPAC name
Cysteine
Other names
2-Amino-3-sulfhydrylpropanoic acid
Identifiers
3D model (JSmol)
Abbreviations Cys, C
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.000.145
EC Number
  • 200-158-2
E number E920 (glazing agents, ...)
KEGG
UNII
  • InChI=1S/C3H7NO2S/c4-2(1-7)3(5)6/h2,7H,1,4H2,(H,5,6) Y
    Key: XUJNEKJLAYXESH-UHFFFAOYSA-N Y
  • InChI=1/C3H7NO2S/c4-2(1-7)3(5)6/h2,7H,1,4H2,(H,5,6)/t2-/m0/s1
    Key: XUJNEKJLAYXESH-REOHCLBHBU
  • InChI=1/C3H7NO2S/c4-2(1-7)3(5)6/h2,7H,1,4H2,(H,5,6)
    Key: XUJNEKJLAYXESH-UHFFFAOYAC
  • C([C@@H](C(=O)O)N)S
  • Zwitterion: C([C@@H](C(=O)[O-])[NH3+])S
Properties
C3H7NO2S
Molar mass 121.15 g·mol−1
Appearance white crystals or powder
Melting point 240 °C (464 °F; 513 K) decomposes
277g/L (at 25 °C) 




Solubility
1.5g/100g ethanol 19 °C 
























+9.4° (H2O, c = 1.3)










Supplementary data page






Cysteine (data page)





Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).



N verify (what is YN ?)





Infobox references








The thiol is susceptible to oxidation to give the disulfide derivative cystine, which serves an important structural role in many proteins. In this case, the symbol Cyx is sometimes used. The deprotonated form can generally be described by the symbol Cym as well.



When used as a food additive, cysteine has the E number E920.



Cysteine is encoded by the codons UGU and UGC.





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