cysteine
noun
cys·te·ine
ˈsi-stə-ˌēn 
: a crystalline sulfur-containing amino acid C3H7NO2S readily oxidizable to cystine
Examples of cysteine in a Sentence
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The regimen included omega-3s; the antioxidant N-acetyl cysteine, commonly referred to as NAC; creatine, an amino acid supplement often used in athletic training; curcumin, an anti-inflammatory supplement derived from the turmeric plant, and more.
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Ryan Coleman, Entertainment Weekly, 26 Jan. 2026
PotMart186 via a Creative Commons license Orange coloration in animals is created by the pigment, pheomelanin, a yellow to reddish-brown pigment synthesized from the amino acid cysteine.
—Grrlscientist, Forbes.com, 16 Jan. 2026
After our first meeting, Kay texted me his hangover regimen, which consists of capsules of N-acetyl cysteine, alpha-lipoic acid, and a supplement called Hangheal Liver Detox.
—Rebecca Mead, New Yorker, 8 Dec. 2025
In a study conducted on mice, scientists from the Massachusetts Institute of Technology (MIT) found that cysteine, a sulfur-containing amino acid, had the strongest rejuvenating effect on stem cells and early-stage intestinal cells, which are often damaged during radiation therapy for cancer.
—Deirdre Bardolf, FOXNews.com, 16 Oct. 2025
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Ryan Coleman, Entertainment Weekly, 26 Jan. 2026
PotMart186 via a Creative Commons license Orange coloration in animals is created by the pigment, pheomelanin, a yellow to reddish-brown pigment synthesized from the amino acid cysteine.
—Grrlscientist, Forbes.com, 16 Jan. 2026
After our first meeting, Kay texted me his hangover regimen, which consists of capsules of N-acetyl cysteine, alpha-lipoic acid, and a supplement called Hangheal Liver Detox.
—Rebecca Mead, New Yorker, 8 Dec. 2025
In a study conducted on mice, scientists from the Massachusetts Institute of Technology (MIT) found that cysteine, a sulfur-containing amino acid, had the strongest rejuvenating effect on stem cells and early-stage intestinal cells, which are often damaged during radiation therapy for cancer.
—Deirdre Bardolf, FOXNews.com, 16 Oct. 2025
See All Example Sentences for cysteine
Cite this Entry
“Cysteine.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/cysteine. Accessed 9 Feb. 2026.
Copy CitationMedical Definition
cysteine
noun
cys·teine
ˈsis-tə-ˌēn
: a sulfur-containing amino acid C3H7NO2S occurring in many proteins and glutathione and readily oxidizable to cystine
—abbreviation Cys
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