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a naturally occurring, nonessential amino acid present in most proteins and synthesized metabolically from phenylalanine. It is a precursor of melanin, catecholamines, and thyroid hormones.

ty·ro·sine (Tyr, Y),

(tī'rō-sēn, -sin),
2-Amino-3-(4-hydroxyphenyl)propionic acid; 3-(4-hydroxyphenyl)alanine; the l-isomer is an α-amino acid present in most proteins.


/ty·ro·sine/ (Tyr) (Y) (ti´ro-sēn) a naturally occurring, nonessential amino acid present in most proteins; it is a product of phenylalanine metabolism and a precursor of thyroid hormones, catecholamines, and melanin.


A nonessential amino acid, C9H11NO3, that is produced in the body from phenylalanine and is a precursor of melanin and of several neurotransmitters and hormones, such as epinephrine and thyroxine.

tyrosine (Tyr)

Etymology: Gk, tyros
an amino acid synthesized in the body from the essential amino acid phenylalanine. Tyrosine is found in most proteins and is a precursor of melanin and several hormones, including epinephrine and thyroxine. See also amino acid, hormone, melanocyte.
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Chemical structure of tyrosine


(Tyr, Y) (tī'rō-sēn)
An α-amino acid present in most proteins.


The AMINO ACID 4-hydroxyphenylalanine. This is one of the 20 amino acids that are incorporated into protein.
Tyrosineclick for a larger image
Fig. 308 Tyrosine . Molecular structure.

tyrosine (Y, Tyr)

one of the 20 AMINO ACIDS common in PROTEINS. It has a polar ‘R’ group structure and is soluble in water. See Fig. 308 . The ISOELECTRIC POINT of tyrosine is 5.7.


A protein building block found in a wide variety of foods that is used by the body to make melanin.
Mentioned in: Albinism

tyrosine (tīˑ·r·sēn),

n an amino acid involved in the synthesis of neurotransmitters; has other functions. Has been used to treat sleep disorders, enhance cognitive function, and alleviate symptoms of ADD. No known precautions. Also called
Enlarge picture
Chemical structure of tyrosine.


(Tyr) (tī'rō-sēn)
An α-amino acid present in most proteins.

tyrosine, tyrosin

Tyr; a naturally occurring amino acid present in most proteins; it is a product of phenylalanine metabolism and a precursor of melanin, catecholamines and thyroid hormones.

tyrosine hydroxylase
an oxidase which converts tyrosine to dopa.
tyrosine tolerance test
used as a test of liver function but about 85% of liver parenchyma must be lost before the test gives a positive reaction.
References in periodicals archive ?
An American expert group (18) has recently reintroduced HT into the core panel of target diseases of screening prognms, using quantification of tyrosine as the basic test.
Protein tyrosine phosphorylation as a mechanism of signalling in mast cells and basophils.
5 [micro]L (volume taken for the PCR step) and analyzed this solution 80 times for tyrosine hydroxylase mRNA.
Observed by immuno-Western blot, six tyrosine phosphorylated proteins were specifically probed by monoclonal-phosphotyrosine antibody (4G10) in testicular lysates of Sprague-Dawley rats (Fig.
5 XLA is caused by 600 different mutations in the Bruton tyrosine kinase (Bkt) gene.
Moser, Modelled Ligand-Protein Complexes Elucidate the Origin of Substrate Specificity and Provide Insight into Catalytic Mechanisms of Phenylalanine Hydroxylase and Tyrosine Hydroxylase, J.
The themes are historical perspectives, principles of cellular signaling by receptor tyrosine kinases (RTKs), specific molecular features and mechanisms of key RTK families, development, and disease and medicine.
Most people with CML have a genetic mutation, called the Philadelphia chromosome, which causes the bone marrow to make an enzyme called tyrosine kinase.
The elimination of drug craving appears to be related to the fact that the enzyme tyrosine decarboxylase is not produced in flies that have mutated genes.
We used an in vitro cuticle bioassay to investigate the effects of 2 alkylphenolic compounds--2,4-bis-(dimethylbenzyl) phenol (compound 3) and bisphenol A (BPA; 4,4'-dihydroxy-2,2-diphenylpropane (also referred to as 4,4'-(propan-2-ylidene) diphenol))--on tyrosine incorporation during the hardening of new cuticle following lobster molting.
Receptor tyrosine kinases are critical signaltransduction mediators regulating essential cellular activities including growth, differentiation and migration, as well as survival and death (1).