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cysteine Syllabification: cys·te·ine
Pronunciation: /ˈsistəˌēn/ /ˈsisˌtēn/

Definition of cysteine in English:


A sulfur-containing amino acid that occurs in keratins and other proteins, often in the form of cystine, and is a constituent of many enzymes.
  • Chemical formula: HSCH2CH(NH2)COOH
Example sentences
  • Whey proteins are also rich in the sulfur-containing amino acids cysteine and methionine.
  • The gelatinase activity was due to metalloproteinases and not cysteine or serine proteinases.
  • The integration of reduced sulphur into the amino acid cysteine is a central step in the assimilation of inorganic sulphur.


Late 19th century: from cystine + -eine (variant of -ine4).

Definition of cysteine in:

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