Cysteine (abbreviated as Cys or C)[3] is a semi-essential[4] proteinogenic amino acid with the formula HO2CCH(NH2)CH2SH>. It is encoded by the codons UGU and UGC. The thiol side chain in Cys often participates in enzymatic reactions, 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.
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| IUPAC name
Cysteine
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| Other names
2-Amino-3-sulfhydrylpropanoic acid
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CAS Number
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52-90-4 52-89-1 (hydrochloride) |
| ChEBI | CHEBI:15356 |
| ChEMBL | ChEMBL54943 |
| ChemSpider | 574 (Racemic) 5653 (L-form) |
| EC Number | 200-158-2 |
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IUPHAR/BPS
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4782 |
| Jmol interactive 3D | Image Image |
| KEGG | D00026 |
| PubChem | 5862 |
| UNII | K848JZ48867ujtytyjtyjjtyjtyrj |
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InChI[show]
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SMILES[show]
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Chemical formula
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C3H7NO2S |
| Molar mass | 121.15 g·mol−1 |
| Appearance | white crystals or powder |
| Melting point | 240 °C (464 °F; 513 K) decomposes |
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Solubility in water
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soluble |
| Solubility | 1.5g/100g ethanol 19 degC [1] |
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Chiral rotation ([α]D)
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+9.4° (H2O, c = 1.3) |
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Structure and
properties |
Refractive index (n), Dielectric constant (εr), etc. |
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Thermodynamic
data |
Phase behaviour solid–liquid–gas |
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Spectral data
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UV, IR, NMR, MS |