cys·​te·​ine ˈsi-stə-ˌēn How to pronounce cysteine (audio)
: a crystalline sulfur-containing amino acid C3H7NO2S readily oxidizable to cystine

Examples of cysteine in a Sentence

Recent Examples on the Web So the scientists exposed the tardigrades to different kinds of molecules known to block cysteine oxidation, as scientists call binding by a free radical. Meghan Bartels, Scientific American, 17 Jan. 2024 The survival mechanism kicks off when cysteines, one of the amino acids that forms proteins in the body, come into contact with these oxygen free radicals and becomes oxidized, the researchers found. Jenna Schnuer, CNN, 5 Feb. 2024 The team noticed that, in particular, the free radicals reacted with cysteine, an amino acid used in protein production. Christian Thorsberg, Smithsonian Magazine, 18 Jan. 2024 Under stressful conditions, with cysteine unavailable to the free radicals being produced, the tardigrades couldn’t form tuns. Meghan Bartels, Scientific American, 17 Jan. 2024 As well as allicin, sulphur compounds including diallyl disulfide and s-allyl cysteine enter your body via the digestive tract and exert impressive antiviral, anti-inflammatory and anti-fungal powers. Georgia Day, Vogue, 1 Dec. 2023 This inhibitor acts as an antagonist of STING by binding to a specific part of the protein — cysteine residue at position 91. William A. Haseltine, Forbes, 13 Nov. 2023 The synthetic form of the amino acid cysteine, NAC has some promising health benefits. Good Housekeeping, 3 Aug. 2023 Some small studies have suggested that NAC supplements may help improve nighttime breathing and reduce snoring in people with sleep apnea.18 Cysteine Deficiency Since cysteine is made in the body and found in high-protein foods, deficiency is rare. Nick Blackmer, Verywell Health, 21 June 2023

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'cysteine.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


International Scientific Vocabulary, from cystine + -ein

First Known Use

1884, in the meaning defined above

Time Traveler
The first known use of cysteine was in 1884

Dictionary Entries Near cysteine

Cite this Entry

“Cysteine.” Dictionary, Merriam-Webster, Accessed 30 May. 2024.

Medical Definition


cys·​teine ˈsis-tə-ˌēn How to pronounce cysteine (audio)
: a sulfur-containing amino acid C3H7NO2S occurring in many proteins and glutathione and readily oxidizable to cystine
abbreviation Cys

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