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.
- ‘The gelatinase activity was due to metalloproteinases and not cysteine or serine proteinases.’
- ‘Whey proteins are also rich in the sulfur-containing amino acids cysteine and methionine.’
- ‘Most of the sulfate substrate comes from sulfoxidation of the amino acid cysteine.’
- ‘As long as the supply of methionine is adequate, cysteine is considered as nonessential.’
- ‘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 -ine).