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-Tyrosine or tyrosine (symbol Tyr or Y) or 4-hydroxyphenylalanine is one of the 20 standard
amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha ...
s that are used by
cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...
to synthesize proteins. It is a non-essential amino acid with a polar side group. The word "tyrosine" is from the Greek ''tyrós'', meaning '' cheese'', as it was first discovered in 1846 by German chemist Justus von Liebig in the protein casein from cheese. It is called tyrosyl when referred to as a
functional group In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the r ...
or side chain. While tyrosine is generally classified as a hydrophobic amino acid, it is more hydrophilic than phenylalanine. It is encoded by the codons UAC and UAU in messenger RNA.


Functions

Aside from being a proteinogenic amino acid, tyrosine has a special role by virtue of the
phenol Phenol (also called carbolic acid) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile. The molecule consists of a phenyl group () bonded to a hydroxy group (). Mildly acidic, it r ...
functionality. It occurs in proteins that are part of signal transduction processes and functions as a receiver of phosphate groups that are transferred by way of protein kinases. Phosphorylation of the hydroxyl group can change the activity of the target protein, or may form part of a signaling cascade via SH2 domain binding. A tyrosine residue also plays an important role in
photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...
. In chloroplasts ( photosystem II), it acts as an electron donor in the reduction of oxidized chlorophyll. In this process, it loses the hydrogen atom of its phenolic OH-group. This radical is subsequently reduced in the photosystem II by the four core manganese clusters.


Dietary requirements and sources

The Dietary Reference Intake (recommended dietary allowance, RDA, i.e. level that considered almost sufficient) for phenylalanine and tyrosine is 42 mg per kilogram of body weight (at the ratio 3:2). For a 70 kg person, this is 2.94 g (phenylalanine + tyrosine). Tyrosine, which can also be synthesized in the body from phenylalanine, is found in many high-
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
food products such as chicken,
turkey Turkey ( tr, Türkiye ), officially the Republic of Türkiye ( tr, Türkiye Cumhuriyeti, links=no ), is a transcontinental country located mainly on the Anatolian Peninsula in Western Asia, with a small portion on the Balkan Peninsula ...
,
fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...
,
milk Milk is a white liquid food produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals (including breastfed human infants) before they are able to digest solid food. Immune factors and immune-modulat ...
, yogurt, cottage cheese, cheese,
peanut The peanut (''Arachis hypogaea''), also known as the groundnut, goober (US), pindar (US) or monkey nut (UK), is a legume crop grown mainly for its edible seeds. It is widely grown in the tropics and subtropics, important to both small an ...
s, almonds,
pumpkin seed A pumpkin seed, also known in North America as a pepita (from the Mexican es, pepita de calabaza, "little seed of squash"), is the edible seed of a pumpkin or certain other cultivars of squash. The seeds are typically flat and asymmetricall ...
s, sesame seeds, soy products and lima beans, but also in avocados and bananas. For example, the white of an egg has about 250 mg per egg,Top 10 Foods Highest in Tyrosine
/ref> while lean beef/lamb/pork/salmon/chicken/turkey contains about 1 g per portion.


Biosynthesis

In plants and most microorganisms, tyrosine is produced via
prephenate Prephenic acid, commonly also known by its anionic form prephenate, is an intermediate in the biosynthesis of the aromatic amino acids phenylalanine and tyrosine, as well as of a large number of secondary metabolites of the shikimate pathway. It ...
, an intermediate on the shikimate pathway. Prephenate is oxidatively decarboxylated with retention of the hydroxyl group to give ''p''-hydroxyphenylpyruvate, which is transaminated using glutamate as the nitrogen source to give tyrosine and α-ketoglutarate. Mammals synthesize tyrosine from the essential amino acid phenylalanine (Phe), which is derived from food. The conversion of Phe to Tyr is catalyzed by the
enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...
phenylalanine hydroxylase, a monooxygenase. This enzyme catalyzes the reaction causing the addition of a hydroxyl group to the end of the 6-carbon aromatic ring of phenylalanine, such that it becomes tyrosine.


Metabolism


Phosphorylation and sulfation

Some of the tyrosine residues can be ''tagged'' (at the hydroxyl group) with a phosphate group ( phosphorylated) by protein kinases. In its phosphorylated form, tyrosine is called phosphotyrosine. Tyrosine phosphorylation is considered to be one of the key steps in signal transduction and regulation of enzymatic activity. Phosphotyrosine can be detected through specific antibodies. Tyrosine residues may also be modified by the addition of a sulfate group, a process known as tyrosine sulfation. Tyrosine sulfation is catalyzed by
tyrosylprotein sulfotransferase Tyrosylprotein sulfotransferase is an enzyme that catalyzes tyrosine sulfation. Function Tyrosylprotein sulfotransferase is the enzyme that catalyzes the sulfation reaction of protein tyrosines, a post-translational modification of prote ...
(TPST). Like the phosphotyrosine antibodies mentioned above, antibodies have recently been described that specifically detect sulfotyrosine.


Precursor to neurotransmitters and hormones

In dopaminergic cells in the
brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...
, tyrosine is converted to L-DOPA by the
enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...
tyrosine hydroxylase Tyrosine hydroxylase or tyrosine 3-monooxygenase is the enzyme responsible for catalyzing the conversion of the amino acid L-tyrosine to L-3,4-dihydroxyphenylalanine (L-DOPA). It does so using molecular oxygen (O2), as well as iron (Fe2+) and t ...
(TH). TH is the rate-limiting enzyme involved in the synthesis of the neurotransmitter dopamine. Dopamine can then be converted into other catecholamines, such as
norepinephrine Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical in the catecholamine family that functions in the brain and body as both a hormone and neurotransmitter. The name "noradrenaline" (from Latin '' ad ...
(noradrenaline) and epinephrine (adrenaline). The
thyroid The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans it is in the neck and consists of two connected lobes. The lower two thirds of the lobes are connected by a thin band of tissue called the thyroid isthmus. The ...
hormones triiodothyronine (T3) and thyroxine (T4) in the colloid of the
thyroid The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans it is in the neck and consists of two connected lobes. The lower two thirds of the lobes are connected by a thin band of tissue called the thyroid isthmus. The ...
are also derived from tyrosine.


Precursor to alkaloids

The latex of '' Papaver somniferum'', the opium poppy, has been shown to convert tyrosine into the
alkaloid Alkaloids are a class of basic, naturally occurring organic compounds that contain at least one nitrogen atom. This group also includes some related compounds with neutral and even weakly acidic properties. Some synthetic compounds of simila ...
morphine Morphine is a strong opiate that is found naturally in opium, a dark brown resin in poppies ('' Papaver somniferum''). It is mainly used as a pain medication, and is also commonly used recreationally, or to make other illicit opioids. T ...
and the bio-synthetic pathway has been established from tyrosine to morphine by using Carbon-14 radio-labelled tyrosine to trace the in-vivo synthetic route.


Precursor to natural phenols

Tyrosine ammonia lyase (TAL) is an enzyme in the natural phenols biosynthesis pathway. It transforms L-tyrosine into p-coumaric acid.


Precursor to pigments

Tyrosine is also the precursor to the pigment ''
melanin Melanin (; from el, μέλας, melas, black, dark) is a broad term for a group of natural pigments found in most organisms. Eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the amino ...
''.


Role in coenzyme Q10 synthesis

Tyrosine (or its precursor phenylalanine) is needed to synthesize the benzoquinone structure which forms part of coenzyme Q10.


Degradation

The decomposition of L-tyrosine (syn. ''para''-hydroxyphenylalanine) begins with an α-ketoglutarate dependent transamination through the tyrosine transaminase to ''para''-hydroxyphenylpyruvate. The positional description ''para'', abbreviated ''p'', mean that the hydroxyl group and side chain on the phenyl ring are across from each other (see the illustration below). The next oxidation step catalyzes by ''p''-hydroxyphenylpyruvate dioxygenase and splitting off CO2
homogentisate Homogentisic acid (2,5-dihydroxyphenylacetic acid) is a phenolic acid usually found in ''Arbutus unedo'' (strawberry-tree) honey. It is also present in the bacterial plant pathogen ''Xanthomonas campestris'' pv. ''phaseoli'' as well as in the ye ...
(2,5-dihydroxyphenyl-1-acetate). In order to split the aromatic ring of homogentisate, a further dioxygenase, homogentisate 1,2-dioxygenase is required. Thereby, through the incorporation of a further O2 molecule, maleylacetoacetate is created.
Fumarylacetoacetate Fumarylacetoacetic acid (fumarylacetoacetate) is an intermediate in the metabolism of tyrosine. It is formed through the conversion of maleylacetoacetate into fumarylacetoacetate by the enzyme maleylacetoacetate isomerase. See also * Fumaryl ...
is created by maleylacetoacetate ''cis''-''trans''-isomerase through rotation of the carboxyl group created from the hydroxyl group via oxidation. This ''cis-trans''-isomerase contains glutathione as a
coenzyme A cofactor is a non- protein chemical compound or metallic ion that is required for an enzyme's role as a catalyst (a catalyst is a substance that increases the rate of a chemical reaction). Cofactors can be considered "helper molecules" that as ...
. Fumarylacetoacetate is finally split by the enzyme fumarylacetoacetate hydrolase through the addition of a water molecule. Thereby fumarate (also a metabolite of the citric acid cycle) and
acetoacetate Acetoacetic acid (also acetoacetate and diacetic acid) is the organic compound with the formula CHCOCHCOOH. It is the simplest beta-keto acid, and like other members of this class, it is unstable. The methyl and ethyl esters, which are quite stab ...
(3-ketobutyroate) are liberated. Acetoacetate is a ketone body, which is activated with succinyl-CoA, and thereafter it can be converted into acetyl-CoA, which in turn can be oxidized by the
citric acid cycle The citric acid cycle (CAC)—also known as the Krebs cycle or the TCA cycle (tricarboxylic acid cycle)—is a series of chemical reactions to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and prot ...
or be used for
fatty acid synthesis In biochemistry, fatty acid synthesis is the creation of fatty acids from acetyl-CoA and NADPH through the action of enzymes called fatty acid synthases. This process takes place in the cytoplasm of the cell. Most of the acetyl-CoA which is co ...
. Phloretic acid is also a urinary metabolite of tyrosine in rats.


Ortho- and meta-tyrosine

Three
structural isomers In chemistry, a structural isomer (or constitutional isomer in the IUPAC nomenclature) of a compound is another compound whose molecule has the same number of atoms of each element, but with logically distinct bonds between them. The term meta ...
of L-tyrosine are known. In addition to the common amino acid L-tyrosine, which is the
para isomer Arene substitution patterns are part of organic chemistry IUPAC nomenclature and pinpoint the position of substituents other than hydrogen in relation to each other on an aromatic hydrocarbon. ''Ortho'', ''meta'', and ''para'' substitution ...
(''para''-tyr, ''p''-tyr or 4-hydroxyphenylalanine), there are two additional regioisomers, namely ''meta''-tyrosine (also known as , L-''m''-tyrosine, and ''m''-tyr) and ''ortho''-tyrosine (''o''-tyr or 2-hydroxyphenylalanine), that occur in nature. The ''m''-tyr and ''o''-tyr isomers, which are rare, arise through non-enzymatic free-radical hydroxylation of phenylalanine under conditions of oxidative stress. m-Tyrosine and analogues (rare in nature but available synthetically) have shown application in
Parkinson's disease Parkinson's disease (PD), or simply Parkinson's, is a long-term degenerative disorder of the central nervous system that mainly affects the motor system. The symptoms usually emerge slowly, and as the disease worsens, non-motor symptoms beco ...
, Alzheimer's disease and arthritis.


Medical use

Tyrosine is a precursor to neurotransmitters and increases plasma neurotransmitter levels (particularly dopamine and norepinephrine), but has little if any effect on mood in normal subjects. A number of studies have found tyrosine is useful during stress, cold, fatigue (in mice), prolonged work and sleep deprivation, with reductions in stress hormone levels, reductions in stress-induced weight loss seen in animal trials, and improvements in cognitive and physical performance seen in human trials. Tyrosine does not seem to have any significant effect on cognitive or physical performance in normal circumstances, but does help sustain working memory better during multitasking.


Interactions

It is unknown if MAOIs interact with tyrosine.


Industrial synthesis

L-tyrosine and its derivatives ( L-DOPA,
melanin Melanin (; from el, μέλας, melas, black, dark) is a broad term for a group of natural pigments found in most organisms. Eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the amino ...
, phenylpropanoids, and others) are used in pharmaceuticals, dietary supplements, and food additives. Two methods were formerly used to manufacture L-tyrosine. The first involves the extraction of the desired amino acid from protein hydrolysates using a chemical approach. The second utilizes enzymatic synthesis from phenolics, pyruvate, and ammonia through the use of tyrosine phenol-lyase. Advances in genetic engineering and the advent of industrial fermentation have shifted the synthesis of L-tyrosine to the use of engineered strains of ''E. coli''.


See also

* Albinism * Alkaptonuria * Betalain * Iodinated tyrosine derivatives * Pauly reaction * Tyramine * Tyrosine sulfation * Tyrosinemia


References


External links


Tyrosine MS Spectrum


* {{Authority control Proteinogenic amino acids Glucogenic amino acids Ketogenic amino acids Aromatic amino acids Phenols Dopamine agonists Carbonic anhydrase activators Monoamine precursors