cysteine

American  

[sis-tee-een, -in] / ˈsɪs tiˌin, -ɪn /

noun

Biochemistry.

1. a crystalline amino acid, C 3 H 7 O 2 NS, a component of nearly all proteins, obtained by the reduction of cystine. Cys; C

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cysteine British  

/ -ɪn, ˈsɪstɪˌiːn /

noun

1. a sulphur-containing amino acid, present in proteins, that oxidizes on exposure to air to form cystine. Formula: HSCH 2 CH(NH 2 )COOH

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cysteine Scientific  

/ sĭs′tə-ēn′ /

1. A nonessential amino acid. Chemical formula: C ₃ H ₇ NO ₂ S.

2. See more at amino acid

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Other Word Forms

• cysteinic
  adjective

Etymology

Origin of cysteine

First recorded in 1880–85; alteration of cystine

Compare meaning

How does cysteine compare to similar and commonly confused words? Explore the most common comparisons:

• cysteine vs. cystine

Example Sentences

See Examples For:

cysteine

The research team is now developing small molecules designed to block cysteine 148 and plans to evaluate them in future preclinical studies.

From Science Daily ● May 31, 2026

The MIT team is now exploring whether cysteine may also support regeneration in other tissues.

From Science Daily ● May 21, 2026

Among all the amino acids tested, cysteine produced the strongest regenerative effect on both stem cells and progenitor cells, which eventually mature into adult intestinal cells.

From Science Daily ● May 21, 2026

They found that a mirror version of cysteine, a sulfur-containing amino acid, can significantly slow the growth of certain tumors while leaving healthy cells largely unaffected.

From Science Daily ● Mar. 12, 2026

Beans have both lysine and tryptophan, but not the amino acids cysteine and methionine, which are provided by maize.

From "1491" by Charles C. Mann