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

Examples of phenylalanine in a Sentence

Recent Examples on the Web These variants are offshoots of Omicron and get their name from their spike protein mutations: The amino phenylalanine (abbreviated as F) replaces the amino acid leucine (abbreviated as L), while the amino acid arginine (R) is replaced by threonine (T). Korin Miller, Verywell Health, 8 May 2024 That’s because those born with PKU have inherited a gene mutation that prevents an enzyme called phenylalanine hydroxylase (PAH) from converting phenylalanine into stuff that your body can use. Bruce Y. Lee, Forbes, 18 Feb. 2024 For example, the primary treatment for phenylketonuria (PKU) is limiting the intake of foods that contain an amino acid called phenylalanine such as meat, dairy, nuts and tofu. Bruce Y. Lee, Forbes, 18 Feb. 2024 The committee further noted that, when consumed, aspartame quickly breaks down in the gastrointestinal tract into three common metabolites: phenylalanine, aspartic acid, and methanol. Beth Mole, Ars Technica, 17 July 2023 With a deficiency of the enzyme, phenylalanine and its metabolites can build up in the blood and damage the brain cells. Dr. Keith Roach, oregonlive, 15 Aug. 2023 August 1974: The FDA receives objections that phenylalanine in aspartame could lead to convulsions and intellectual disabilities. Ananya Bhattacharya, Quartz, 14 July 2023 For now, the only strong health advisory against aspartame is for people with phenylketonuria (PKU) who can't break down the protein phenylalanine which is found in aspartame. Stephanie Brown, Verywell Health, 13 July 2023 High-quality protein is any protein that contains all of the nine essential amino acids (histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine) that our bodies don’t make on their own. USA TODAY, 2 July 2023

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'phenylalanine.' 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

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 13 Jun. 2024.

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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