tyrosine

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tyrosine

(tī`rəsēn), organic compound, one of the 20 amino acidsamino acid
, any one of a class of simple organic compounds containing carbon, hydrogen, oxygen, nitrogen, and in certain cases sulfur. These compounds are the building blocks of proteins.
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 commonly found in animal proteins. Only the l-stereoisomer appears in mammalian protein. It is not essential to the human diet, since it can be synthesized in the body from phenylalaninephenylalanine
, organic compound, one of the 22 α-amino acids commonly found in animal proteins. Only the l-stereoisomer appears in mammalian protein.
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. When the enzyme that catalyzes the transformation of phenylalanine to tyrosine is not active because of a hereditary defect, the serious disease known as phenylketonuriaphenylketonuria
(PKU), inherited metabolic disorder caused by a deficiency in a specific enzyme (phenylalanine hydroxylase). The absence of this enzyme, a recessive trait, prevents the body from making use of phenylalanine, one of the amino acids in most protein-rich foods, and
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 (PKU) results. Other defects in tyrosine metabolism include the rare hereditary disorder known as alkaptonuria, characterized by discharge of a urine which darkens on standing exposed to air. Tyrosine is a precursor of the adrenal hormones epinephrineepinephrine
, hormone important to the body's metabolism, also known as adrenaline. Epinephrine, a catecholamine, together with norepinephrine, is secreted principally by the medulla of the adrenal gland.
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 and norepinephrinenorepinephrine
, a neurotransmitter in the catecholamine family that mediates chemical communication in the sympathetic nervous system, a branch of the autonomic nervous system.
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 as well as of the thyroid hormones, including thyroxinethyroxine
, substance secreted by the thyroid gland. The hormone thyroxine forms by combining the amino acid tyrosine with iodine. Complexed to a protein, it is stored in the follicle stems between thyroid cells.
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. Melaninmelanin
, water-insoluble polymer of various compounds derived from the amino acid tyrosine. It is one of two pigments found in human skin and hair and adds brown to skin color; the other pigment is carotene, which contributes yellow coloring.
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, the skin and hair pigment, is also derived from this amino acid. Tyrosine residues in enzymes have frequently been shown to be associated with active sites. Modification of these residues with various chemicals often results in a change in the specificity of the enzyme toward its substrates or even in total destruction of its activity. In 1846 tyrosine was obtained as a product of the degradation of the protein casein (from cheese). It was synthesized in the laboratory in 1883, and its structure was thus determined.

Tyrosine

 

[β-(para-hydroxyphenyl)alanine; oxyphenylaminopropionic acid], an amino acid. Tyrosine exists in the form of optically active D-and L-forms and the racemic DL-form. L-tyrosine is a constituent of many proteins and peptides, such as casein, fibroin, keratin, and insulin. It is readily isolated from protein hydrolysates because of its poor solubility in water. Phosphate esters of L-tyrosine are also components of proteins.

Tyrosine is a replaceable amino acid that is formed in animals and humans by the enzymic oxidation of phenylalanine. Disruption of this process gives rise to a serious hereditary disease, phenylpyruvic oligophrenia. The oxidation of tyrosine by the enzyme tyrosinase is an important intermediate reaction in the biosynthesis

of melanins, norepinephrine, and epinephrine in humans. The iodinated derivatives of tyrosine—thyroxine and triiodothyronine—are thyroid hormones.

Tyrosine performs an important function as a precursor in the biosynthesis of alkaloids, such as morphine, codeine, and papaverine. The enzymic oxidation of L-tyrosine is used to obtain the drug L-dopa. The breakdown of tyrosine in the body, in which ascorbic acid plays a role, results in the formation of fumarte and acetoacetic acids, which are incorporated into the Krebs cycle in the form of acetyl coenzyme A.

REFERENCES

Meister, A. Biokhimiia aminokislot. Moscow, 1961. (Translated from English.)
Lehninger, A. Biokhimiia. Moscow, 1974. (Translated from English.)

E. N. SAFONOVA

tyrosine

[′tir·ə‚sēn]
(biochemistry)
C9H11NO3 A phenolic alpha amino acid found in many proteins; a precursor of the hormones epinephrine, norepinephrine, thyroxine, and triiodothyronine, and of the black pigment melanin.
References in periodicals archive ?
Differential effects of diabetes on adipocyte and liver phosphotyrosine and phosphoserine phosphatase activities.
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Phosphorylation of VEGFR-2 was visualized with PY20 phosphotyrosine antibodies (UBI), and equal loading of lysates was confirmed with [beta]-actin antibodies (Santa Cruz Biotechnology).
Differentiation: interleukin-1/toll NF-[KAPPA]B, nuclear hormone receptor, apoptosis, receptor phosphotyrosine phosphatase
Antibody for phosphotyrosine (PY20) was obtained from Sigma-Aldrich.
The blots were blocked with 3% gelatin in TBS for 2 hr at room temperature and probed with antibodies against phosphothreonine, phosphoserine, or phosphotyrosine (PY99) overnight at 4[degrees]C.
Structure and ligand recognition of the phosphotyrosine binding domain of Shc.
Blotting Ab against phosphotyrosine (pTyr, clone 4G10) and biotin-conjugated Ab 4G10 were from Upstate Biotechnology Inc.
Results of Sunesis' research are available in an advance online publication ("Discovery of a New Phosphotyrosine Mimetic for PTP-1B using Breakaway Tethering") of the May 14, 2003 edition of the Journal of the American Chemical Society (JACS).