phe·​nyl·​al·​a·​nine ˌfe-nᵊl-ˈa-lə-ˌnēn How to pronounce phenylalanine (audio)
: an essential amino acid C9H11NO2 that is converted in the normal body to tyrosine

Example Sentences

Recent Examples on the Web The nine essential amino acids are: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Amber Smith, Discover Magazine, 16 Nov. 2022 For the trial, the company enrolled 20 adults with high phenylalanine levels. WIRED, 7 Nov. 2022 The classic success story is neonatal screening for phenylketonuria [a genetic disorder characterized by the inability to utilize the amino acid phenylalanine], which has saved thousands of children’s brains. Robert Keating, Discover Magazine, 15 Dec. 2010 Without the enzyme, phenylalanine can rise to dangerously high levels that damage the brain. Ryan Cross,, 15 Nov. 2022 People with the disorder can’t break down an amino acid called phenylalanine—or Phe for short—which is found in high-protein foods like meat and eggs. WIRED, 7 Nov. 2022 He was born with phenylketonuria (PKU), the build-up of amino acid called phenylalanine in the body which can cause learning disabilities. Eric Walden, The Salt Lake Tribune, 10 Aug. 2022 The test offered a way to detect high levels of phenylalanine, the amino acid that builds up in PKU. Mark Johnson,, 29 Apr. 2022 If a person had large amounts of phenylalanine in the blood, the disease's signature, bacteria would proliferate; otherwise the bacteria would be held in check. Mark Johnson,, 29 Apr. 2022 See More

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'phenylalanine.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

Word History


International Scientific Vocabulary

First Known Use

circa 1883, in the meaning defined above

Time Traveler
The first known use of phenylalanine was circa 1883

Dictionary Entries Near phenylalanine

Cite this Entry

“Phenylalanine.” Dictionary, Merriam-Webster, Accessed 5 Feb. 2023.

Medical Definition


phe·​nyl·​al·​a·​nine ˌfen-ᵊl-ˈal-ə-ˌnēn, ˌfēn- How to pronounce phenylalanine (audio)
: an essential amino acid C9H11NO2 that is obtained in its levorotatory L-form by the hydrolysis of proteins (as lactalbumin), that is essential in human nutrition, and that is converted in the normal body to tyrosine
abbreviation Phe
see phenylketonuria, phenylpyruvic acid

More from Merriam-Webster on phenylalanine

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