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

Recent Examples on the Web

Spot On! Advertisement Advertisement There are also 11 non-essential amino acids—alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine—that can be produced by your body. —Stacey Colino, Time, 27 May 2025

That being said, the researchers point out that eliminating cysteine from human diets is all but impossible because the amino acid is found in nearly all foods. —Michael Franco may 21, New Atlas, 21 May 2025

Rich in vitamin C and may help boost glutathione levels Eggs: Contain the amino acid cysteine that the body uses to produce glutathione Nuts: Include the essential mineral selenium that can bolster glutathione production A Word From Verywell Taking steps to prevent a hangover is key. —Cristina Mutchler, Verywell Health, 10 Apr. 2025

Glutathione is a protective antioxidant composed of three amino acids: cysteine, glutamic acid and glycine. —Adrianna Rodriguez, USA TODAY, 6 Feb. 2025

Word History

Etymology

International Scientific Vocabulary, from cystine + -ein

First Known Use

1884, in the meaning defined above

Medical 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